한국자기학회지 (Journal of the Korean Magnetics Society) (Journal of the Korean Magnetics Society)
한국자기학회 (The Korean Magnetics Society)
- 격월간
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- 1598-5385(pISSN)
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- 2233-6648(eISSN)
과학기술표준분류
- 물리학 > 입자/장물리
Aim & Scope
The published articles in the Journal of the Korean Magnetics Society are academic research papers in either Korean or English, and their topics include the magnetic theory, magnetic materials and their properties, magnetic recording materials and technology, spin electronics, measurements and applications, and other relevant topics. The papers in the Journal of the Korean Magnetics Society are classified into three categories; academic research articles, academic review articles, and technical reviews.
http://www.komag.org/jkms KSCI KCI제5권5호
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An overview will be given on recent Mossbauer and magnetization investigation of the applied field dependence of the magnetic properties of typical systems without strong magnetic anisotropy and showing the absence of magnetic saturation in high fields (including iron-rich spin glass (amorphous
$Fe_{93}Zr_{7}$ , soft ferromagnets (amorphous$Fe_{88}Zr_{12}$ ,$Fe_{70}Ni_{20}Zr_{10}$ and$Fe_{88}B_{12}$ ) and pure Fe). The results emphasize that shape anisotropy due to surface irregularities causes misalignment between the magnetization and the applied field in the otherwise collinear magnetic structure. -
The physical origins of anomalous volume effect (Invar effect) and elastic effect (Elinvar effect) are critically examined. We found that, unlike the volume effect, the shear elastic properties are not much influenced by the ferromagnetic transition. This finding shows that the two anomalies originate from different physical origins, thus contradicting the conventional wisdom. We discuss the consequences of this finding in the light of recent experiments.
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Measurements of X-ray diffuse scatterings were made in disordered single crystal of Fe-28.3 at%Pt Invar alloy around a 200-Bragg peak in a wide temperature range between 15 K and 300 K. Observed diffuse scatterings were almost spherical, suggesting a homogeneous disordered alloy. However, the qdependence of the observed thermal diffuse scattering was different from the usual type, indicating a possibility of existence of local distortion of lattice accompanied by a large gradient of stress.
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We have investigated the quasi-two-dimensional magnetism for the layered transition metal compound (C/sub n/H/sub 2n+1/NH/sub 3/)/sub 2/CuCl/sub 4/ (n=10, 14) in the high temperature regions by means of EPR (Electron Paramagnetic Resonance) and SQUID measurements. As a result, the magnetic transitions were reflected in the EPR linewidths and the magnetic suceptibilities in a sensitive manner. Fluctuations of the magnetic susceptibility and a similar variation of the .DELTA. g =(g/sub .parallel. -/g/sub .perp. /)g/sub .parallel. / value were also observed around the structural phase transition temperatures.
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Yoshida, H.;Fujimori, H.;Kaneko, T.;Abe, S.;Watanabe, K.;Matsumoto, M.;Yoshida, T.;Kanomata, T. 362
The magnetic properties for$Fe_{24}Pt_{76}\;and\;Fe_{26}Pt_{74}$ have been investigated. The temperature vs. magnetic susceptibility curve for$Fe_{24}Pt_{76}$ had no peak near the Neel temperature. The magnetization proccess at 4.2 K showed only a linear variation up to the high magnetic field of 240 kOe. That for$Fe_{26}Pt_{74}$ at 77 K showed a metamagnetic transition at 100 kOe. These properties were discussed on the basis of a band picture. -
High performance magnetic materials are characterized by the combination of outstanding magnetic properties and optimized microstructures, e.g., nanocrystalline composites of multilayers and small particle systems. The characteristic parameters of the hysteresis loops of these materials vary over more than a factor of
$10^{6}$ with optimum values for the coercive field of several Tesla and permeabilities of$10^{6}$ . Within the framework of the computational micromagnetism (nanomagnetism) using the finite element method the upper and lower bounds of the coercive field of different types of grain ensembles and multilayers have been determined. For the case of nanocrystalline composites the role of grain size, exchange and dipolar coupling between grains and the degree of grain alignment will be discusses in detail. It is shown that the largest coercivities are obtained for exchange decoupled grains, whereas remanence enhancing requires exchange coupled grains below 20 nm. For composite permanent magnets based on$Nd_{2}Fe_{14}B$ with an amount of ~ 50% soft$\alpha$ -Fe-phase coercivities of${\mu}_{0}H_{c}=0.75\;T$ , a remanence of 1.5 T and an energy product of$400\;kJ/m^{3}$ is expected. In nanocrystalline systems the temperature dependence of the coercivity is well described by the relation${\mu}_{0}H_{c}=(2\;K_{1}/M_{s}){\alpha}-N_{eff}{\mu}_{0}M_{s}$ , where the microstructural parameters$\alpha$ and$N_{eff}$ take care of the short-range perturbations of the anisotropy and$N_{eff}$ is related to the long-range dipolar interactions.$N_{eff}$ is found to follow a logarithmic grain size size dependence${\mu}_{0}H_{c}=(2\;K_{1}/M_{s}){\alpha}-N_{eff}(\beta1nD){\mu}_{0}M_{s}$ . Several trends how to achieve the ideal situation$\alpha$ ->1 and$N_{eff}$ ->1->0 will be discussed. -
The magnetization pattern of the central cross section deduced from the ac susceptibility measurement is described with an analytical function. The function is based on a charge-free configuration. The thickness of the
$^{\circ}$ wall lying in a (100) plane and the wall energy are calculated analytically. Total energy of the domain structure has been minimized with Ritz's method. As the result of the minimization, the energy density of the$^{\circ}$ wall lying in a (100) plane is$0.58\;erg/cm^{2}$ and the one for a (110) plane is$1.18\;erg/cm^{2}$ . Thicknesses of these walls are calculated numerically. Also, the calculation indicates there is a small central domain at the cross section without applied current. With the ac susceptibility measurement the existence of the domain without current can be identified. -
Employing the muffin-tin-orbital theory combined with pseudo-potential concepts, we have evaluated hybridization matrix elements between R and T sites in
$RT_{2}$ compounds. The matrix elements are calculated with two parameters, the interatomic distance between R and T atoms from the crystal structure data, and the expectation values of the radial distances for the radial wave functions of the ground state charge densities, which are obtained from the linearized muffin-tin orbital band method within the local density approximation. It is found that the R 4f/T 3d hybridization matrix elements decrease with an increasing atomic number from R=Ce to Gd, and that they are smaller in$RNi_{2}$ than in$RCo_{2}$ , which are consistent with trends observed in recent photoemission spectroscopy experiments. It is also found that the magnitudes of the hybridization matrix elements in$RFe_{2}$ are comparable to those in$RNi_{2}$ . -
The pressure dependence of the Curie temperature was determined in 2-dimensional like ferromagnet, MnAlGe up to a maximum pressure of 7.5 Gpa through measurements of electric resistance vs temperature curves. The pressure coefficient was positive with a considerably high rate of 9 K/GPa in the low pressure ragion, while it decreased gradually down to one order of magnitude smaller value at the maximum pressure. It was concluded that ther is an upper limit of about 550 K in the super-exchange type ferromagnetic interaction between Mn layers.
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A universal dispersion equation for magnetostatic waves(MSW) propagating in the film with arbitrary-multiple magnetic layers magnetized in an arbitrary direction was derived with a matching boundary condition method. The computing result curves of delay time were shown.
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We have developed a new method for measuring the M-H hysteresis loop of a spheroid-shape magnetic material having a uniaxial anisotropy and discussed its accuracy at fields near the coercivity. Our torque magnetometric method simultaneously gives the saturation magnetization and the remnant magnetization. Furthermore, the coercivity depending on the applied field orientation is accurately measured by this simple technique. An accuracy of the present method is negligibly affected even at fields near the coercivity, where the magnetization is not uniform. The technique makes a torque magnetometer an extremely high sensitive tool for measuring M-H hysteresis loop.
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Simultaneous measuring system for permeability and resistivity of magnetic sheets is presented. In this system, the coil impedance is measured when a specimen is inserted between two coils. This system was applied to nickel sheets, iron-nickel alloys and a nickel film.
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For the core loss measurement under arbitrary waveform of magnetic induction, we have constructed a single sheet core loss measuring system which consists of yoke apparatus for single sheet of
$10\;cm{\times}10\;cm$ , arvitrary waveform synthesizer, B-feedback system, and two channel transient recorder. Using the constructed measuring system, we can measure core loss including higher harmonics up to 2 kHz. Core loss of non-oreinted electrical steel was increased exponentially when higher harmonic frequency was increased or amplitude of harmonic induction was increased. -
The prospects for further improvement in the energy product of permanent magnets are discussed. Some current research directions, including artificial nanostructures, nitride magnets and novel flux sources are briefly reviewed.
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Magnetic properties of model exchange-spring magnets, which are composed of magnetically soft and hard grains, were calculated by means of computer simulation. The dependence of the magnetic properties on the strength of intergrain exchange interaction and the amount of soft grains was studied. The existence of soft grains enhanced the remanence remarkably, and the remanence over
$0.8M_{s}$ was obtained in the model magnets containing 25% or more soft grains by volume. The calculated coercivity vs. the strength of the exchange interaction curves showed a peak at a critical strength of the exchange interaction, although the remanence increased monotonously with increase in the strength of the exchange interaction. Thus the maximum energy product also reached a peak around the same critical strength. The calculated maximum energy product exceeded$300kJ/m^{3}$ when the magnet is assumed to be composed of$Fe_{3}B$ and$Nd_{2}Fe_{14}B$ . -
Microstructure and magnetic properties of
$Fe-Nd_{13.5}-Co_{15}-B_{6-8}Ga_{0-1}-Zr_{0.2-1}$ alloys during HDDR process were studied.$ZrB_{2}$ phase was detected and identified by X-Ray diffraction. Influence of Ga, Zr and Ga+Zr additions on phase relations at different stages of HDDR process was studied by X-ray diffraction and magnetic measurements. -
By adding 1wt.%
$HfB_{2}$ into$Nd_{3-4}Fe_{77-78.5}B_{18.5}$ alloys, the grain growth of$Fe_{3}B/Nd_{2}Fe_{14}B$ composite phases during annealing was found to be hindered by 40~50%. It is proposed that the addition of$HfB_{2}$ leads to the formation of fine dispersoids of$HfB_{2}$ in the$Fe_{3}B/Nd_{2}Fe_{14}B$ composite magnet. The maximum energy product($(B.H)_{max}$ ) as well as intrinsic coercivity($_{i}H_{c}$ ) for the$Nd_{3}Fe_{78.5}B_{18.5}\;+\;1wt.%\;HfB_{2}$ alloy were enhanced by more than 25%$(B.H)_{max}=10\;MGOe,\;_{i}H_{c}=2.5\;kOe)$ due to the addition of$HfB_{2}$ while remanent magntization($B_{r}$ ) was reduced slightly. Itis deduced that the formation of fine dispersoids will also play a role of magnetic domain pinning. -
An attempt has been made to investigate the mechanism of magnetic alignment in the magnets produced by upset forging the
$Pr_{20}Fe_{74}B_{4}Cu_{2}$ cast bulk alloy. Upset forging of the cast alloy was carried out for 20 sec to an 80 % thickness reduction (strain rate :$4{$\times}10^{-2}s^{-1}$ ) in an open die configuration at varying temperatures in the range$600^{\circ}-900^{\circ}C$ . It has been found that the upset forging process at temperatures above$800^{\circ}C$ can achieve a magnetic alignment to a great extent from copper-containing Pr-Fe- B-type cast ingot. The growth manner of the ferromagnetic$Pr_{2}Fe_{14}B$ matrix grain in Pr-Fe-B-type alloys was studied by examining the morphology change of the matrix grain in sintered body, and it was found that the matrix grains grew in anisotropic manner such that the grain grew more rapidly along the a- or b-axis than along the c-axis. This anisotropic grain growth led to the plate-like shape of the matrix grain. The magnetic alignment during the upset forging was attributed to grain boundary gliding of the plate-like grains, and the geometry of the grains in the cast ingot and the presence of a large amount of the praseodymium-rich grain boundary phase were thought to play a key role in the achievement of magnetic alignment. -
The magnetic properties of the hot-pressed magnets made from the Fe-Nd-B alloys, mechanically ground and subsequently blended with binary additives such as Al-Cu and Ag-Zn before hot pressing, were investigated. The coercivities of the magnets increased as the concentration of Al-Cu increased up to 1 wt.% or up to 3 wt.% in the case of Ag-Zn. At higher concentrations the coercivities decreased markedly. The maximum gain in coercivity by the addition was about 20 %. typical values of
$_{i}H_{c}$ and$B_{r}$ of a hotpressed magnet containing 1 wt.% Al-Cu were 18 kOe and 7 kG, respectively. It was found that Cu, Ag, and Zn, which diffused into the magnet during hot pressing, were mostly concentrated on the Nd-rich grain boundary phase whereas Al was present not only in the grain boundary region but also in the matrix grains. -
The influence of Nd and B contents on the magnetic properties and structures of
${\alpha}-Fe$ based Nd-(Fe,Co)-B-Mo-Cu alloys was investigated.$Nd_{4}{(Fe_{0.9}Co_{0.1})}_{92-x}B_{x}Mo_{3}Cu_{1}$ and$Nd_{x}{(Fe_{0.9}Co_{0.1})}_{86-x}B_{10}Mo_{3}Cu_{1}$ amorphous alloys prepared by rapid solidification process were crystallized to form nanocrystalline structure. The increase of B content in$Nd_{4}{(Fe_{0.9}Co_{0.1})}_{92-x}B_{x}Mo_{3}Cu_{1}$ nanocrystalline resulted in the change of stucture of soft phase in the sequence of${\alpha}-Fe$ ->${\alpha}-Fe+Fe_{3}B$ ->$Fe_{3}B$ . The coercivitis of the alloys were increased with increasing B content and was 263 kA/m at x=18. On the contrary, the remanence has shown an opposite trends. The increase of Nd content in$Nd_{x}{(Fe_{0.9}Co_{0.1})}_{86-x}B_{10}Mo_{3}Cu_{1}$ nanocrystalline containing${\alpha}-Fe$ as main phase had no effect on the structure and improved coercivity up to 256 kA/m. However, the remanence was decreased from 1.4 T to 1.15 T according to the increase of Nd content. -
The hydrogen decrepitation behaviour of the
$Sm_{2}Fe_{17} alloy containing 4at%Nb was examined by means of DTA and SEM metallography, and the magnetic properties of the alloy were studied by means of VSM or TMA. It has been found that a simple hydrogenation and degassing treatment for the alloy caused a poor hydrogen decrepitation. The cycle treatment consisting of repeated hydrogenation and degassing, however, caused a severe hydrogen decrepitation with a combination of intergranular and transgranular failure. The disproportionation temperature of the hydrogenated$Sm_{2}Fe_{17} -type alloy was enhanced significantly by small addition of Nb. It has also been found that the Curie temperature of$Sm_{2}Fe_{17} matrix phase in the Nb-containing alloy has been enhanced by the hydrogenation, and this was attributed to the increase in interatomic distance between the neighbouring iron atoms caused by the interstitial occupancy of the hydrogen atom into the$Sm_{2}Fe_{17} -type lattice. The magnetisation of the$Sm_{2}Fe_{17} alloy containing Nbwas found to be lower than that of the Nb-free alloy, and this was explained by the dilution effect due to the presence of the paramagnetic$Sm_{2}Fe_{17} phase. -
THE SPIN REORIENTATION AND THE MAGNETI ANISOTROPY IN
$R_{2}Fe_{17-x}M_{x}C_{y}$ (R=Er, Tm, M=Al, Ga)In order to consider the change of the magnetic anisotropy energy by the Al or Ga substitution for Fe, spin reorientation temperature$T_{SR}$ and Curie temperature$T_{c}$ in$R_{2}Fe_{17-x}M_{x}$ (R=Er, Tm, M=Al, Ga) have been studied both experimentally and theoretically. As a result,$T_{SR}$ and$T_{c}$ for$R_{2}Fe_{17-x}M_{x}$ shift toward higher temperature side with x ($0{\leq}x{\leq}2.0$ ). The${\Delta}T_{c}$ the difference of the$T_{c}'s$ between$Er_{2}Fe_{17-x}Al_{x}$ and$Tm_{2}Fe_{17-x}Al_{x}$ , is always about 10 K independent of Al-content. But in the case of Ga substitution, the${\Delta}T_{c}$ increases with Ga-content ; especially, the${\Delta}T_{c}$ for x=2.0 is 43 K. This value of the${\Delta}T_{c}$ is not explained by only the difference of the de Gennes fator G between$Er^{3+}$ and$Tm^{3+}$ , but it is thought that the values of$J_{ErFe}$ and$J_{TmFe}$ themselves are not equal. ($J_{AB}$ : the exchange interaction between A and B.) -
Electronic structures of Fe overlayers on Cr(Fe/Cr) films, with an Fe coverage of
$1-20{\AA}$ , have been investigated by using photoemission spectroscopy. Experimental results are compared with supercell band structure calculations for a system with monolayer (ML) Fe on each side of five layer Cr, Fe(1ML)/Cr(5ML)/Fe(1ML). The extracted Fe 3d partial spectral weight in Fe/Cr exhibits very interesting features for very thin Fe overlayers. First, a sharp emissionnear the Fermi energy is observed, which is expected to originate primarily from hybridization between Fe and Cr 3d electrons at the Fe/Cr interface, and partially from the Fe 3d surface states in the Fe overlayer. Second, other structures are observed at higher binding energies which resemble the Cr 3d valence bands, also suggesting large hybridization between Fe and Cr 3d states at the Fe/Cr interface. These conjectures are confirmed by band structure calculations for Fe(1ML)/Cr(5ML)/Fe(1ML). -
Using Boltzmaan equation by introducing the potential barrier scattering which buit by Hall-effect, a possible origin of giant magnetoresistance in multilayers is proposed. The calculated results may be well explain the giant magnetoresistance observed in multilayers.
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The composition and thickness dependence and the ferromagnetic under- and overlayer effect on the magnetoresistance ratio and saturation field of the Co-Ag nano-granular films were investigated. The maximum magnetoresistance (23% at R.T.) in the as-deposited state was obtained in the
$3000{\AA}$ $Co_{30} Ag_{70}$ bare alloy film. As the thickness of the alloy films decreased below$500{\AA}$ , the MR ratio decreased because of the resistivity increase and the non-uniform film formation. We showed that the ferromagnetic over- and underlayer could reduce the saturation field of the nano-granular films via exchange coupling effect. The magnetoresistance and the saturation field of the$100{\AA}$ alloy film were 3.65 % and 2.85 kOe respectively and those of the under- and overlayered alloy films with$200{\AA}$ Fe were 3.3 % and 1.23 kOe respectively. -
Giant magnetoresistance(GMR) of
$Cu_{85-x}Co_{15}Ni_{x}$ melt-spu ribbons is closely correlated with the microstructure produced by the spinodal decomposition. The solid solution range is extanded by the replacement of Cu by Ni in the as-quenched state. The wavelengths obtained by subsequent isothermal aging in Cu-Co-Ni ribbons are shorter than those in Cu-Co binary ribbons, resulting in the increase of the surface-to-volume ratio. The largest MR ratio of 8 % in high field has been achieved in the$Cu_{80}Co_{15}Ni_{5}$ aged ribbon. The field dependence of MR ratio in low fields becomes larger with the Ni content. -
We have investigated the effects of sputtering Ar gas pressure on magnetic anisotropy of Co/Pt multilayers, where sputtering Ar gas pressure was varied from 2 to 20 mTorr. The surface and volume anisotropies were found to be strongly dependent on sputtering Ar gas pressure. In particular, the surface anisotropy exhibited more than fourfold enhancement as Ar pressure was decreased from 20 to 5 mTorr. We have found that the surface anisotropy was closely correlated with the low-angle x-ray diffraction intensity. We believe that these results are mainly ascribed to the variation of microstructure in the Co/Pt multilayer thin films with sputtering Ar gas pressure.
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We have investigated the effects of deposition angle on structural and magnetic properties of e-beam evaporated
${(4-{\AA}\;Co/9.2-{\AA}\;Pt)}_{23}$ multilayer thin films prepared on tilted substrates. It was found that the [111] crystallographic orientations of the multilayer thin films were not aligned with colummar growth orientations and they were remained to be normal to the substrate planes even though the deposition angle was severely oblique up to$60^{\circ}$ . The analysis of the torque curve reveal that the intrinsic anisotropy energy was monotonically decreased with the deposition angle but the easy axis orientation parallel to the substrate normal was not much influenced by deposition angle. -
We have constructed an apparatus for in sity measurement of stress of the film prepared by sputtering using an optical noncontact displacement detector. A Change of the gap distance between the detector and the substrate, caused by stress of a deposited film, was detected by a corresponding change of the reflectivity. The sensitivity of the displacement detector was
$5.9\;{\mu}V/{\AA}$ and thus, it was turned out to be good enough to detect stress caused by deposition of a monoatomic layer. The apparatus was applied to in situ stress measurements of Co/X(X=Pd or Pt) multilayer thin films prepared on the glass substrates by dc magnetron sputtering. At the very beginning of the deposition, both Co and X sublayers have subjected to their own intrinsic stresses. However, when the film was thicker than about$100{\AA}$ , constant tensile stress in the Co sublayer and compressive stress in the X sublayer were observed, which is believed to be related to a lattice mismatch between the matching planes of Co and X. -
Granular Fe-SiO films were prepared by co-evaporating in a vacuum. Magnetic properties of the films were investigated by
$M\"{o}ssbauer$ and magnetization measurments. The$M\"{o}ssbauer$ data suggest that the films consist of amorphous Fe-Si alloy particles with the size of nanometers. Superparamagnetic magnetization curves were well reproduced by considering the distribution of particle size and the magnetic dipole interaction between particles as the mean field. -
The iron-based Metglas 2605S3A amorphous alloy ribbons are annealed at
$435^{\circ}C$ for various periods from 5 to 210 min, and the effect of annealing is investigated on the dc magnetic properties of the ribbon. Typical square-type hysteresis loops are observed for the ribbons annealed fo 5 min, indicative of the nearly complete removal of residual stresses which are produced during melt-quenching. As the annealing time increases, the coercivity increases and the shape of hysteresis loops transforms to round type and finally to sheared one at the longest annealing time of 210 min. These results may be explained by the formation of clusters with chemical shortorder and very fine crystallites (at the annealing time of 210 min), and the diffusion-induced stresses during the formation of the clusters. For the samples annealed for 5 min, very good dc properties of the squareness ratio, coercivity and maximum permeability are observed, but, rather unexpectedly, the initial permeability is found to be very low. These results are considered to be due to a simple domain structure consisting of very small number of$^{\circ}$ domains. -
Soft magnetic properties of Fe-based (Fe,Co)-B-Al-M (M=Nb, Mo or Ta) nanocrystalline alloy have been investigated. The alloy obtained directly form the rapid solidification process. Microstructure of the alloy is a mixtu re of ultrafine bcc Fe(Co) nanocrystallines and a small amount of retained amorphous phase. Heat treatment of as-prepared alloys improves soft magnetic properties in high frequency range.
${(Fe_{.85}Co_{.15})}_{70}B_{18}Al_{10}Ta_{6}$ alloy alloy annealed at$500^{\circ}C$ for 1 h shows the most improved soth magnetic properties among the alloy examined. Average grain size of the nanocystalline is about 10 nm. -
With the object of developing a new magnetic core materials for high frequency use, the crystallization behaviors and the soft magnetic properties of amorphous
$F_{86-x}Al_{4}B_{10}Zr_{x}\;(5{\leq}x{\leq}10\;at%)$ alloys subjected to annealing treatment at wide temperature range were investigated. For optimally annealed$Fe_{86-x}Al_{4}B_{10}Zr_{x}$ alloys in amorphous state, rather good soft magnetic properties of${\mu}_{e}=17000~25000,\;H_{c}=20~30$ mOe and$B_{10}{\geq}0.6$ T are obtained. However, as the alloys crystallize, the soft magnetic properties are largely dergely deteriorated, which is attributed principally to the narrow temperature gap between$T_{x1}$ and$T_{x2}$ , which allows the nearly co-precipitation of bcc phase and Fe-B compounds in incipient crystallization stage. -
The crystallization behaviors and magnetic properties for
$Fe_{81-x}Al_{4}B_{10}Zr_{5}Cu_{x}$ (x=0, 1, 2 at%) alloys is investigated. By the addition of 1~2 Cu, the temperature range, where a single bcc phase exists, expands largely over 200 K and the grain size of bcc phase represents to less than 10 nm. For the optimally annealed Cu-added alloys, the high$\mu_{e}$ (1 kHz) above 20000 combined with the high$B_{10}$ of about 1.4 T is obtained in nanocrystalline state. The low core loss of 95.8 W/kg at 0.1 T and 100 kHz is confirmed for the nanocrystalline$Fe_{80}Al_{4}B_{10}Zr_{5}Cu_{1}$ alloy. -
Amorphous
$Co_{80+x}TM_{12}B_{8-x}$ (TM = Ti, Zr, Hf, Nb and x = 0, 2, 4 at%) alloys were prepared by single roll melt spinning technique. Saturation magnetization of the amorphous ribbons was measured by SQUID and vibrating sample magnetometer from 5 to 800 K under applied fields up to 10 kOe. Typical thermo-magnetization curves were observed and the average values of the spectroscopic splitting g factor were estimated from the ferromagnetic resonance curve. For all the amorphous alloys studied here the saturation magnetization in the temperature range 5 K up to about$0.3T_{c}$ can be described by the Bloch relation:$M_{s}(T)\;=\;M_{s}(0)(1-BT^{3/2}-CT^{5/2})$ . From the values of$M_{s}(0)$ , B and spectroscopic splitting g factor the spin wave stiffness constants were calculated. -
The magnetic properties of ultrathin
$Fe_{84}B_{9}Nb_{7}$ nanocrystalline ribbon alloy with the thickness of$7-14\;\mu\textrm{m}$ were investigated. It was found that the effective permeability at the frequency over 100 kHz increased with decreasing ribbon thickness. Moreover the core loss decreased considerably with reduction of the ribbon thickness. The effective permeability at 1 MHz and the core loss at 1 MHz and 0.1 T for$Fe_{84}B_{9}Nb_{7}$ alloy with the thickness of$7\;\mu\textrm{m}$ were 3,700 and 2.7 W/cc, respectively. The reduction of thickness to less than$10\;\mu\textrm{m}$ was found to be very effective in obtaining high permeability and low core loss in the MHz frequency range. It was considered that the improvement of magnetic properties in the high frequency range was due to the reduction of the eddy current. -
By means of adding B into Sendust alloy (Fe-Si-Al) with state of amorphous ribbon, mechnical properties of alloy was improved effectively, and magnetic properties didn't decrease obviously. The optimum adding quantity of B is 0.015-0.03 wt%. The adding of B was thought to give rise to reduction of ordering degree of
$Fe_{3}(Si,Al)$ phase of Sedust alloy(Fe-Si-Al-B) and result in improvment of embrittlement of this alloy. -
A heat-treatment method of pre-annealing and then flash annealing(FA) has been used to improve the soft magnetic properties of nanocrystalline
$Fe_{76}CuSi_{13}B_{10}$ and$Fe_{74}CuNb_{3}Si_{12}B_{10}$ alloys. Outstanding magnetic properties of nanocrystalline$Fe_{74}CuNb_{3}Si_{12}B_{10}$ alloy were attained by flash-annealing in air after annealed at$500^{\circ}C$ for 0.5hr below the crystallization temperature. The same results were obtained for$Fe_{74}CuSi_{13}B_{10}$ alloy. The measurment of relief of stress and X-ray diffraction were used to analyze the effect of flashannealing. -
The crystallization kinetics of
$Fe_{73.5}Si_{13.5}B_{9}Cu_{1}Nb_{3}$ amorphous alloy has been investigated using differential scanning calorimetry (DSC). The crystallization process had two stages, i.e. precipitation of the$\alpha$ -Fe(Si) solid solution and the tetragonal borides. The isothermal transformation data of the amorphous alloy has been fitted successfully to the generalized Johnson-Mehl-Avrami equation. The mean time exponent, n, obtained is close to 2.5. The value of n=2.5 may be interpreted as being due to a diffusion-controlled transformation process with a constant nucleation rate, one likely transformation mode for the crystallization of metallic amorphous alloys. The activation energy of the overall crystallization process deduced from the time to 50% crystallization are about 81 kcal/mole. The value is of the same order as those estimated from viscous flow. -
We have studied the magnetization in fields up to 1T at 5K, the saturation magnetization dependence on temperature and the temperature dependence of AC-susceptibility at very low fields (5mOe to 50mOe) of glassy
$Fe_{91-x}Zr_{7}B_{2}Ni_{x}$ (x = 0, 5, 10, 15) alloys. The temperature dependence of the magnetization follows the predictions of spin wave excitations with long wavelengths. At zero Ni concentration there is a clear competition between ferromagnetic and antiferromagnetic interactions giving rise to spin-glass behaviour. The addition of Ni drastically modifies the magnetic properties: the antiferromagnetic exchange coupling is reduced and finally disappears, the spin wave stiffness increases from 39.5 to$87.3\;meV{\AA}^{2}$ and To increases from 230 K to 478 K. We develop a simple model to quantify the competing interactions and to relate the antiferromagnetically coupled Fe moments to the Ni concentration. We find that the initial susceptibility increases with increasing Ni content along with a decrease of the temperature dependence. -
The Fe-TM-C-N nanocrystalline films (TM : Hf, Zr and Nb) are investigated to examine the relation between microstructure and soft magnetic properties. In these films, as the atomic radius of TM element increases,
$P_{N2}$ which was added to get good soft magnetic properties was decreased and the maximum value of the permeability shifted to the high Fe range in the composition diagram. The best soft magnetic properties achieved in these films are : Hc of 0.15 Oe,$\mu_{eff}$ of 7800 (1MHz) and$4{\pi}M_{s}$ of 17.5 kG in Fe-Hf-C-N film ; Hc of 0.06 Oe,$\mu_{eff}$ of 2750 (1MHz) and$4{\pi}M_{s}$ of 16.8 kG in Fe-Zr-C-N film and Hc of 0.31 Oe;$\mu_{eff}$ of 2100 (1MHz) and$4{\pi}M_{s}$ of 15.5 kG in Fe-Nb-C-N film. It was considered that the stronger the bonding force between TM and C(N), the finer TM(C,N) phase is precipitated and therefore, the finer$\alpha$ -Fe grains are formed. The effective permeability of the Fe-Zr-C-N films and Fe-Nb-C-N films remains nearly constant up to 10 MHz. -
The temperature dependence of spin wave mode separation in amorphous
$Co_{89.5}Zr_{10.5}$ thin film has been investigated at temperatures between 100 K and 300 K. The magnetization and the spectroscopic splitting factor were obtained for the main resonance mode in parallel and perpendicular magnetic field.${\Delta}H_{2-3}$ , the difference between resonance field of mode 2 and the resonance field of mode 3, increases with decreasing temperature. The linewidth increases for all the modes with decreasing temperature. Especially in mode 3 it increases rapidly below 200 K. This phenomenon could be caused by the increase of exchange stiffness constant or the decrease of surface magnetic anisotropy constant with decreasing temperature. -
Ferromagnetic resonance experiments have been used to investigate the magnetic properties of amorphous
$Co_{89.5}Zr_{10.5}$ thin films deposited by DC magnetron sputtering method. In the thickness range from$350\;{\AA}$ to$3,200\;{\AA}$ , measurements were carried out in a static magnetic field perpendicular and parallel to the film plane and in a conventional 9.44 GHz spectrometer at room temperature. The ferromagnetic resonance spectra by the field perpendicular to the film plane showed standing spin wave. The spacing and the relative intensities between the various spin wave resonance peaks are analysed considering surface magnetic anisotropy. The surface magnetic anisotropy constant ($K_{so},\;K_{sd}$ ) of amorphous$Co_{89.5}Zr_{10.5}$ thin films are$0.02\;erg/\textrm{cm}^2$ and$0.55\;erg/\textrm{cm}^2$ respectively regardless of the film thickness except for$3,200\;{\AA}$ film. In case of$3,200\;{\AA}$ these values are$0.46\;erg/\textrm{cm}^2$ and$0.55\;erg/\textrm{cm}^2$ respectively. -
The stress in Permalloy thin films fabricated by rf magnetron sputtering on the Si (100) substrates has been investigated with various deposition parameters such as the film thickness, argon pressure, and rf power. The internal stress changes from compressive to tensile with higher input power and argon pressure. The cause of stress variations with these deposition parameters is discussed in terms of thermal and/or intrinsic stress changes. Low coercive force is obtained from Permalloy thin films at a condition of low compressive stress.
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The etching characteristics of magnetic thin films of permalloy and Fe-based alloys are investigated. The thin films are fabricated by rf magnetron sputtering and the substrates used are silicon and glass. Etching is done by ion beam technique and the main process parameters investigated are beam voltage, beam current and accelerating voltage. The etch rate of the magnetic films is proportional to the beam current, but it is not directly related to the accelerating voltage and beam voltage. The dependence of etch rate on the process parameters can be explained by ion current density. It is found that the ion beam etching is effective in obtaining well-developed micro-patterns on the permalloy and Fe- based magnetic thin films.
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A set of
$Fe_{1-x}Ni_{x}$ (x=0.10, 0.25, 0.30, 0.35, 0.50, 0.60, 0.75, 0.85) fine particles prepared by the gas evaporation technique was studied by$M\"{o}ssbauer$ , XRD and other techniques. The XRD and$M\"{o}ssbauer$ patterns of the sample with x=0.10 ($Fe_{90}Ni_{10}$ ) were found to be exceptionally different, showing an austenite phase stability when the particles are quenched. This phase stability is quite different from that of the corresponding bulk alloy. Using binomial distrbution fits of the$M\"{o}ssbauer$ spectra of the particles in terms of nearest and next nearest neighbour configurations around the Fe atoms, an analysis of this phase stability is given. The changes in the relative intensities of the resulting magnetic sextets are used to determine the increase in martensite following the austenite-martensite transformation process. The stable austenite can, therefore, be determined. This stability may be related to the oxide surface layer and the small number of atoms of these fine particles. -
The effect of Cu substitution on the properties of NiZn ferrites sintered at low temperature with composition is investigated. The densification of NiCuZn ferrite in dependent upon Cu content in the composition of (N/sub 0.5-x/Cu/sub x/ Zn/sub 0.5/O)(Fe/sub 2/O/sub 3/)/sub 0.98/. Electrical resistivity is maximum at x=0.2. Dispersion characteristics of complex permeability of (Ni/sub 0.5-x/ Cu/sub x/Zn/sub 0.5/O)(Fe/sub 2/O/sub 3)/sub 0.98/ is observed above x=0.3 and relaxation frequency increases with higher temperature. The magnetic loss of NiCuZn ferrite is occurred above the Cu content x=0.3 at a low frequency.
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The magnetic properties of Mg-Mn ferrites were investigated in the composition range of
$Mg_{a}Mn_{b}Fe_{c}O_{4\pm\delta}$ (a+b+c=3) with the addition of$Al_{2}O_{3}$ . In$MgO-MnO-Fe_{2}O_{3}$ ternary system, the spinel single phase existed within the composition range of MgO-50 mol%, MnO-70 mol% and$Fe_{2}O_{3}-60\;mol%$ . The saturation magnetic flux density increased with the increase of$Fe_{2}O_{3}$ content and showed the maximum at the stoichiometric composition of$(Mg,Mn)Fe_{2}O_{4}$ . In$Mg_{x}Mn_{1-x}Fe_{2}O_{4}(x=0.2~0.8)$ system, the saturation magnetic flux density showed the maximum at$Mg_{0.2}Mn_{0.8}Fe_{2}O_{4}$ . The addition of$Al_{2}O_{3}$ resulted in the decrease of saturation magnetic flux density but increased the electrical resistivity. -
The absorption properties of Cu-Zn ferrite/rubber composite microwave absorbers with PZT(Lead Zirconate Titanate) additive were evaluated. The composite specimens have prepared by molding and curing the mixture of matrix rubber and Cu-Zn ferrite powders which are synthesized by the coprecipitation method using Fe Cl/sub 3/ .center dot. 6H/sub 2/O, CuCl/sub 2/ .center dot. 2H/sub 2/O and Zn Cl/sub 2/ as a starting raw materials. PZT is used as another filler particles to adjust the material constants of Cu-Zn ferrite/rubber composite specimens. We have found that the material constants of specimens could be controlled by various PZT mixing ratio. On the Cu-Zn ferrite/rubber composite specimens with PZT 10[wt%] additive, the reflection losses were larger than 30[dB] in the frequency range from 2.72 to 4.4[GHz]' by adjusing the thickness.
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Additional magnetooptical Kerr effect (AMOKE) was observed in several multilayer structures. For Fe/Pd and Co/Cu Multilayers, AMOKE enhanced the Kerr rotation in short wavelength side, while for Fe/Ag and FeSi/Cu multilayer systems the Kerr rotation enhancement appeared in long wavelength side. A number of ferromagnetic/nonmagnetic/ferromagnetic(FM/NM/FM) sandwiches showed that the AMOKE led to oscillations of Kerr rotation and Kerr ellipticity in certain wavelength range with changing NM layer thickness similar to the oscillatory interlayer coupling. The oscillation of effective optical constants related to the MOKE oscillation was observed for the first time. The mechanisms of the AMOKE were discussed.
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By using the ac field source which can change the applied field magnitude, frequency and dc offset field, the dynamic magnetoresistance characteristics of permalloy based multilayers which have different R-H(resistance-magnetic field) curves were monitored and compared with static magnetoresistance curves that were measured with electromagnet of VSM. Output of each sample according to the external field strength was identified and optimum bias position could be obtained.
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Magnetoresistance of NiFeCo/Cu/NiFeCo/FeMn uncoupled exchange biased sandwiches has been studied. The magnetoresistance change ratio,
${\Delta}R/R_{s}$ showed 4.1 % at a saturation field as low as 11 Oe in$Si/Ti(50\;{\AA})/NiFeCo(70\;{\AA})/Cu(23\;{\AA})/NiFeCo(70\;{\AA})/FeMn(150\;{\AA})/Cu(50\;{\AA})$ spin valve structure. In this system, the magnetoresistance was affected by interlayer material and thickness. When Ti and Cu were used as the interlayer material in this structure, maximum magnetoresistance change ratio were 0.32 % and 4.1 %, respectively. 6.1 % MR ratio was obtained in$Si/Ti(50\;{\AA})/NiFeCo(70\;{\AA})/Cu(15\;{\AA})/NiFeCo(70\;{\AA})/FeMn(150\;{\AA})/Cu(50\;{\AA})$ spin valve structure. The magnetoresistance change ratio decreased monotonically as the interlayer thickness increased. It was found that the exchange bias field exerted by FeMn layer to the adjacent NiFeCo layer was ~25 Oe, far smaller than that reported in NiFe/Cu/NiFe/FeMn spin valve structure(Dieny et. al., ~400 Oe). The relationship between the film texture and exchange anisotropy ha been examined for spin valve structures with Ti, Cu, or non-buffer layer. -
X-ray magnetic-circular-dichroism (MCD) spectra, orbital (
$ ) and spin magnetic moments ($ $ ) for Co(110) monolayers a free standing mode or sandwiched between Pd(Pd/1Co/Pd)and Cu layers (Cu/1Co/Cu) are calculated using the thin film full potential linearized augmented plane wave energy band method. In contrast to the double peak structure predicted for the Co(0001) surface, only a minor side peak is found in the MCD spectra for Cu/Co/Cu, while MCD spectra for the other systems show a single peak structure. The MCD sum rules originally derived from a single ion model are found in the band approach to be valid for the systems investigated. However, for the spin sum rule, the magnetic dipole term ($ $ ) is not negligible and needs to be included.$ -
The use of amorphous magnetic alloys as tags or targets in electronic article surveillance systems such as antishoplifting desvices is briefly reviewed. Improved tags became possible with the discovery in 1988 of asymmetric magnetization reversal (AMR) in certain amorphous alloys annealed in applied field approximately equal to the earth's field. These asymmetric hysteresis loops are highly unusual, if not unique, and so greatly diminish the probability of false alarms in a detection system. furthermore, the jump field Hj, which is the coercive field in negative applied fields, can be controlled over a useful range by controlling the field applied to the sample during annealing. By applying several tags to an object, each with a different jump field, it is possible to identify the object with a numeric code that can be remotely read by nonoptical means.
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Fe rich nanocrystals embedded in an amorphous magnetic matrix have been shown to exhibit outstanding soft magnetic properties. The cause of softness in the exchange coupling between the two-phases. In this paper some effects of the exchange coupling between the nanocrystals and the matrix are reviewed.
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In the present paper some of the magnetic properties of the nanocrystalline Fe-based magnets produced by an appropriate annealing of their metallic glass precursors are reviewed. These properties are discussed on the grounds of their characteristics measured at the elevated temperatures. It is shown that the effective magnetostriction these magnets display, results from the competition among two contributions of the opposite sign originating from the individual magnetic phases, crystalline phase and the residual glassy matrix in which the nanocrystallites are embedded. It is also shown that at certain conditions the magnets considered expose superparamagnetic behavior and that their isothermal magnetization characteristics can successfully be used to calculate the distribution of the particle volumes. Application of the recently invented new genetic algorithm method, a powerful tool to calculate these distributions is, finally, presented.
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The effects of surface oxidation on magnetic properties were investigated at high frequencies (10k-100MHz) for
$7-18\mu\textrm{m}$ thick$Co_{70}Fe_{5}Si_{15}B_{10}$ amorphous ribbons with controlled domain structure. Oxidation was accelerated by acid-treatment or anodic oxidation treatment, and the insulation layers were prepared on the surfaces of the ribbons. The acid-treatment was effective in improving permeability and magnetic loss. Although the anodic oxidation treatment was effective in both making oxide layer and thinning, the magnetic properties were not improved compared with the case of the acid-treatment. -
Magnetic properties of FeTaN and FeTaC films deposited by DC magnetron reactive sputter were investigated, and correlated with their microstructures. The optimum magnetic properties of Hc : 0.25 Oe, Bs : 14.5 kG, and
${\mu}'$ : 4000 (5MHz) are observed in the$Fe_{78.8}Ta_{8.5}N_{12.7}$ film, and Hc : 0.25 Oe, Bs : 14.5 kG, and${\mu}'$ : 2700 (5MHz) in the$Fe_{75.6}Ta_{8.1}C_{16.3}$ film. In both FeTaN and FeTaC films with minimum grain size show the best soft magnetic properties. Thermal stability of the soft magnetic properties of FeTaN is found to be higher than FeTaC for similar compositons. TaN and TaC particles form to retard the growth of$\alpha$ -Fe grains. TaN particles in FeTaN show higher efficiency in retarding the grain growth during heat treatments resulting the higher thermal stability, compared to TaC particles in FeTaC films. -
Ferrite cores are often magnetized under DC-biased field because they have been intensively used in electronic circuits such as an inverter circuit and a switching regulator circuit. Thus we investigated the effects of DC-biased field on magnetic properties in the frequency range of DC-100kHz for two kinds of ferrite cores, TDK PC38 and TDK
$H_{3}S$ , which have different shapes of B-H loop from each other. The magnetic loss per cycle, W/f, in the$H_{3}S$ core decreased with increasing the strength of DC-biased field, although W/f in the PC38 core increased monotonically with DC-biased field. The observed decreasing tendency differs from the previous result for Si-Fe and ferrite cores, and can be attributed to decrease in eddy current loss as well as that in hysteresis loss. -
The effect of processing parameters such as milling, additives and sintering atmoshpere on the magnetic properties of Mn-Zn ferrite was investigated. The experiment was followed by general ceramic fabrication process and added additives were
$CaCO_{3}$ ,$SiO_{2}$ ,$V_{2}O_{5}$ ,$ZrO_{2}$ , and$Nb_{2}O_{5}$ . The effects of additives could be divided into three categories which were formation ofliquid phase, substitution in lattice and inducing stress. Core loss smong the magnetic properties was dependent mainly on the additives and also correlated with processing parameters. As a result, an optimum condition of preparing process for a high quality Mn-Zn ferrite was suggested by controlling the correlation of each processing parameters. -
Thin CoCrTa/Cr films were deposited on glass substrates at
$280^{\circ}C$ with or without Al underlayer. The coercivity of CoCrTa increased considerably by introducing an Al underlayer. The grain size of Cr thin film deposited on Al underlayer became smaller than that of Cr thin film deposited on glass substrate. The grain size of CoCrTa thin film was determined by Cr grain size. The cause of the coercivity increase seems to be associated with the refinement and uniform distribution of CoCrTa grains. -
We studied the effects of Pt and Cr addition in a new Co-Cr-P-Pt alloy system with the coercivity higher than 2000 Oe even when they were deposited without substrate heating and bias voltage. The coercivity of the films increased from 1000 to 2000 Oe or higher by addition of 12 at.%Pt. The variation of the anisotropy field with increasing Pt content was similar to that of the coercivity. This indicate that the increase of the coercivity might be associated with increase of the anisotropy field with Pt addition. With the addition of Cr, the coercivity of the films increased up to 8 at.%Cr and the coercive squareness of the films decreased. The angular variation of coercivity deviated at a lower angle from domain wall motion mode as the Cr content increases. From these result, it is believed that the grain isolation of the films is enhanced with the addition of Cr.
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High coercivity thin
$Fe_{3}O_{4}$ and${\gamma}-Fe_{2}O_{3}$ films were deposited on Si substrate under well controlled$O_{2}$ partial pressure by dcreactive magnetron sputtering. The coercivity of as-deposited maggnetite films is below 640 Oe. After cxidizing at$360^{\circ}C$ for 10 minutes, the films transform to maghemite${\gamma}-Fe_{2}O_{3}$ completely, and the coercivity increases greatly to 2100~4120 Oe, depending on modification of not with minor addition of Co or/and Mn. The orign of coercivity enhancement is attributed mainly to magnetic anisotropy arisen from interfacial stress. The addition of 5 at% Co and 5 at% Mn greatly enhances coercivity and squareness ratio. These films are potential for ultra-high density recording applications. -
BaM films have a lot of advantage of chemical stability and mechanical stability as compared with a metallic thin film. In this paper, (Ba.Pb)M films have been prepared by using dc magnetron sputtering system and the dependences of their crystallographic characteristics and magnetic properties on oxygen pressure(
$Po_{2}$ ) were studied. The films prepared at$Po_{2}$ of around 0.02mTorr exhibit a fine particle-like structure and${\Delta}{\theta}_{50}$ is as small as$1^{\circ}$ .$Hc_{\bot},\;Hc_{//}$ and Ms of (Ba.Pb)M films are 700-800Oe, 200Oe and 180-230emu/cc, respectively. -
Longitudinal magnetic recording process of thin film media was simulated by the 2-D finite element method (FEM). To describe precisely the hysteresis behavior of thin film media, scalar Preisach model was used. In this paper, we discussed the formation of bit patterns and importance of modeling of minor loops in high density recording. The effects of the media coercivity and film thickness on the remanent magnetization and transition shape were investigated.
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FeN thin films were deposited on glass by RF diode reactive sputtering. The films were annealed in the air and in vacuum. The film annealed in the air showed sharp decrease of saturation magnetization and change of easy axis direction to hard axis direction and vice versa after
$300^{\circ}C$ anneal. The coercivity decreased down to 0.5 Oe after$400^{\circ}C$ anneal. After$450^{\circ}C$ anneal, the film showed${\varepsilon}-Fe_{2-3}N$ phase. The films annealed in vacuum showed coercivity increase after$300^{\circ}C$ anneal for the film deposited with initial substrate temperature of$35^{\circ}C$ and after$400^{\circ}C$ anneal for the film deposited with initial substrate temperatue of$170^{\circ}C$ . These films showed$Fe_{16}N_{2}$ X-ray peaks after$450^{\circ}C$ anneal. -
We have studied the effect of the nitrogen on the microstructure, thermomagnetic properties and corrosion resistance of Fe-Hf-C-N nanocrystalline thin films with high permeability and high saturation magnetization. These films were fabricated by reactive sputtering in
$Ar+N_{2}$ plasma using an rf magnetron sputtering apparatus. As$P_{N2}$ increases, the microstructure changes from amorphous to crystalline$\alpha$ -Fe phase and again returns to amorphous one. Spin wave stiffness constant increases with$P_{N2}$ until 5%$P_{N2}$ , and then decreases with the further increase. This trend corresponds well with that of the microstructure with increasing$P_{N2}$ . The Fe-Hf-C-N films with over 3%$P_{N2}$ show higher corrosion resistance than the N-free Fe-Hf-C films. The Fe-Hf-C-N films are considered to have high potentials for the head core materials suitable for high density recording systems, owing to their excellent soft magnetic properties and corrosion resistance. -
The depletion of thin liquid films due to the combined effect of centrifugation, surface roughness, and air-shear has recently been studied. While surface roughness of a rotating solid disk can be represented by deterministic cures, it has been argued that spatial random processes provide a more realistic description. Chiefly because of surface roughness, there is an asymptotic limit of retention of a thin film flowing on the rotating disk. The aim of this article is to model the depletion of thin-film flow and analyze the interplay of centrifugation, surface tension, viscosity, air-shear, disjoining pressure, and surface roughness that affect the depletion of the film. Also, the robustness of stochastic description of surface roughness is examined.
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In digital video recording, higher areal density is strongly required for realizing digital VCRs. In order to accomplish higher areal density. we have implemented a system that has a narrow track pitch and can record data of about 30 Mbps(15 Mbps per channel) with the conventional S-VHS tapes. After computer simulation using the characteristics of the experimental system, we have selected appropriate equalizer and detection method by taking into account performance and cost (including hardware complexity). As a result, the selected equalizer and detection schemes are cosine equalizer and integrated de tection, respectively. The implemented system confirms reliable operation with a symbol error rate of less than
$1{\times}10^{-4}$ . In this paper, We will show the performance of the implemented system together with simulation results. -
Magnetization behavior of sputter-deposited Co/Pd multilayers were characterized, and it has been found that even when the multilayers are sputtered at low pressure (10 mTorr), the coercivity of the multilayers can be increased to large extent without noticeable change of saturation magnetization by increasing the deposition pressure of Pd underlayer. It turned out that the surface topology of Pd underlayer gets rough as deposition pressure increases, which consequently affects the magnetization reversal mode of Co/Pd multilayers from domain wall motion to magnetic spin rotation. The enhancement of coercivity is attributed to the domain wall pinning effect which is comected with the surface roughness of Pd underlayer on which Co/Pd multilayers grow.
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Co-ferrite (
$CoO-Fe_{2}O_{3}$ ) thin films have been prepared by two ways of low temperature solid reaction including oxidation process, being based on$Co-layer/{\alpha}-Fe_{2}O_{3}$ films and$Co-layer/Fe_{3}O_{4}$ films. Magnetic properties of both Co-ferrite films have been measured and compared. The samples from$Co-layer/Fe_{3}O_{4}$ films have a large coercive force in the direction perpendicular and have a great poler kerr rotation angle at wavelength 700 nm than ones from$Co-layer/{\alpha}-Fe_{2}O_{3}$ films. The typical magnetic properties are as follows; saturation magnetization$4{\pi}Ms$ , 2.9 kG; remnant magnetization$4{\pi}Mr$ , 2.0 kG; coercive force Hc, 4.0 kOe; kerr rotation angle${\PHI}k$ , 0.39 deg($\lambda\;=\;700\;nm$ ); and initial magnetization energy E,$3.3\;{\times}\;10^6\;erg/\textrm{m}^3$ , respectively. -
The domain wall motion coercivity,
$H_{c}$ , of magnetic materials arises from the dependence of the wall energy on localized changes in material parameters (magnetization, anisotropy, exchange energy densities). However, in an otherwise perfectly homogeneous material, the domain wall energy might change due to the change in the volume of the wall versus the wall position. Thus, any surface roughness contributes to the coercivity. Assuming different two-dimensional surface profiles, characterized by average wavelengths${\lambda}_{x}$ and${\lambda}_{y}$ , and relative thickness variations dh/h, the coercivity due to the surface roughness has been calculated. Compared to the one dimensional case, the 2D coercivity is reduced. Depending on the ratio of${\lambda}$ to the domain wall width,$H_{c}$ has a maximum around 2, and increasing with dh/h. With the decreasing thickness of the thin film and GMR heads, it might be the domain factor in determining the coercivity. -
The viscometric technique is used to study the effects of microstructure on the viscosity (viscosity vs. concentration or shear rate) of magnetic particle suspensions. In this characterization, measurement of suspension viscosity is used to obtain the dependence of viscous energy dissipation on microstructural state of dispersions. Microstructural shape effects which are related to particle orientation are then indirectly obtained. Empirical formulas from mean field theory and the Mooney equation, which are applicable at high concentration of magnetic particles, are used to relate viscosity to particle concentration. The validity and physical meaning of these equations are discussed.
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The magnetic separation of Nd-Fe-B powders prepared by melt-spun and HDDR processes was investigated. The experiments show that the ununiform melt-spun powders can be separated into various standards by means of magnetic separation method. The magnetic powders with higher properties were obtained by the use of suitable separating field. For example, the properties of ununiform melt-spun powders are Br=7.95 kG, iHc=9.93 kOe and (BH)max=10.2 MGOe before separating. Through separating in different magnetic fields, the powders obtained with a separating field of 780 Oe has the optimum properties of Br=7.7 kG, iHc=11.0 kOe and (BH)max=15.3 MGOe. The magnetic properties of the HDDR magnetic powder are hardly separated by the magnetic separation method.
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The observed high-field magnetization curves of
$Sm_{2}Fe_{17}N_{3.0}$ at 4.2 K and 296 K are well reproduced by the calculation using the Sm-Fe exchange field$2\mu\textrm{B}H_{ex}\;=\;320\;K$ and two crystalline electric field parameters${A_{0}}^{2}=\;-910\;K$ and${A_{1}}^{0}=\;200\;K$ . The calculation shows that during the magnetization process along the hard axis at 4.2 K, the Sm moment rotates toward the direction antiparallel to H when H < 110 kOe and then returns to the field direction with further increase of the field. At 296 K, the Sm moment rotates toward the direction antiparallel to H monotonously with increasing field and finally becomes antiparallel to H when$H{\geq}H_{A}=210\;kOe$ . The particular magnetization process of the Sm moment can be explained by the field-induced noncollinear coupling between the spin and orbital moments of the Sm ion. -
Using by the x-ray diffractometry(XRD), the thermomagnetic analysis(TMA), a scanning electron microscopy (SEM-EDX), we knew that the
$(Sm_{0.5}RE_{0.5})Fe_{11}Ti$ (RE=Ce,Pr,Nd,Sm,Gd,Tb) compounds were formed to tetragonal$ThMn_{12}$ -type structure having a uniaxial magnetocrystalline anisotropy with easy magnetization c-axis. The intrinsic magnetic properties of those were determined by fitting the two magnetization curves of experimental and calculation magnetization. The anisotropy constant$K_{1}$ of this compounds was in the range of$1.75\;-\;9.2\;MJ/m^{3}$ and approximately one order higher than$K_{2}$ .$SmFe_{11}Ti$ had the highest anisotropy of$K_{1}\;=\;9.2\;MJ/m^{3}$ ,$K_{2}\;=\;0.4\;MJ/m^{3}$ and${\mu}_{o}H_{A}=\;19.8\;T$ among the compounds, substitution of any other rare earth elements for Sm decreased magnetocrystalline anisotropy. -
Our team works on mixture of hard magnetic materials. As hard magnetic material we used mixture of powders: melt-spun ribbon Nd-Fe-B, ferrite and Alnico. Their different mixtures are basic material for dielectromagnets under our investigation. Main disadvantage of dielectromagnets with Nd-Fe-B alloy powder as a component is a low corrosion resistance. Protection against corrosion is covering dielectromagnets with metallic or organic coating film. The coating film protects dielectromagnets from free particles on the surface and low resistance for mechanical stresses too. The surface of dielectromagnets prepared from mixture of powders if formed by metallic particles - powder of Nd-Fe-B and Alnico, particles of oxide - powder of ferrite and particles of resin - bonding materials. Team work on technology of laying the metallic coating on dielectromagnets prepared from mixture of mentioned powders. Papers show the results of initial investigation on metallic coating technology. It shows influence of type and used technology of the metallic coating film on magnetic properties of dielectromagnets.
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Reducing media noise is a key to realizing high areal recording density. However, perpendicularly oriented Co-Cr films, stong candidates for high density recording media, have received little attention in terms of recording noise. We studied the noise characteristics of Co-Cr based alloy films by varying the compositionally separated structure. Co-Cr films with fine compositionally separated microstructure were observed to have low noise, which recording density dependence were negative or week. Studies on control of the microstructure and magnetic properties in combination with noise analysis are important to realize high density recording media.
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Fundamental issues and general procedures of modeling the head disk interface (HDI) in order to provide design criteria for future ultra-low flying sliders are given. Intermittent contact and gaseous rarefaction effects are discussed using nonconventional kinetic theory. To illustrate the simulation results, we modeled IBM 3370 taper flat sliders and positive/negative "bow tie" sliders. Several alternative HDI concepts for future disk drives - viscoelastic bearings, a hybrid system, and contact recording - are also briefly discussed.
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In this paper we review recent work in our laboratory on nanocomposite CoSm-based films including CoSm with Cr underlayer (CoSm//Cr), exchange-coupled magnetic films consisting of CoSm and FeCo layers (CoSm/FeCo), and CoSm multilayers with nonmagnetic spacing layers of SmO (CoSm/SmO). The emphasis is on detailed investigations of microstructure and magnetic properties for CoSm//Cr films, exchange-spring effects for CoSm/FeCo films, and interlayer effects for (CoSm/ SmO) multilayers.
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Magnetic domains were observed using an image lock-in technique for backscattered electron contrast (Type II) with a 200 kV scanning electron microscope. Backscattered electrons indicate a difference in magnetic domain structures at the upper and lower parts of the upper pole in thin-film heads, changing the acceleration voltage. With this method, it is also possible to observe the domain structure of the thin-film head pole through a 10 to
$20\;\mu\textrm{m}$ protective layer, and the upper shield of the MR head through the coil in the resist, alumina overcoat, and upper pole. -
Pd/(Pt/Co/Pt) modulated multilayer films have been deposited on various substrates with Pd/Pt buffer layers. Films grown at different temperatures have very distinct magnetic properties and surface microstructures. Atomic force(AFM) and scanning tunneling (STM) microscopies studies of these films reveal that films deposited at room temperature have small grain structures with an average grain size of about
$140\;{\AA}$ . However, much larger grains of about$1200\;{\AA}$ in size are observed in the films grown on buffer layers which were deposited at$500^{\circ}C$ . These large grains are found to actually consist of smaller grains of about$170{\AA}$ in diameter. SQUID magnetic and Kerr hysteresis loop measurements indicate that multilayer films with large grains exhibit high magnetic coercivities of around 5 kOe. A subgrain growth model is proposed to understand the observed grain structures in the multilayers. -
Bi-substituted gadolinium iron garnet films were deposited on GGG(111) and NGG (111) substrates by irradiating KrF excimer laser onto targets having compositions of
$Bi_{x}Gd_{3-x}Fe_{5}O_{12}$ ($2.0{\leq}x{\leq}3.0$ ) under substrate temperature of$580~620^{\circ}C$ . Analysis on structure, composition and angle of Faraday rotation,${\theta}_{F}$ , were carried out. The composition, the structure and the magneto-optical properties of the obtained films were found to be strongly dependent both on the compositions of the targets and on the pressure of oxygen. Before annealing in air, all films showed${\theta}_{F}{\geq}0$ at${\lambda}=6328{\AA}$ , while several films showed${\theta}_{F}{\leq}0$ after the annealing. The highest value of Bi-substitution up to x = 1.76 with uniform composition was obtained. -
We investigated the effects of Sm on the microstructure and magnetic properties of Fe-Co Alloy films prepared by a DC triode sputtering. The magnetostriction was found to be changed with the Sm content from positive to negative values, taking a zero magnetostriction was at about 3 at% Sm. The Sm content dependence of magnetostriction was explained by the formation of Sm enriched amorphous phase surrounding the main bcc (Fe,Co) crystalline phase, which was observed by a high resolution transmission electron microscopy.
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The variation of magnetic permeability and dielectric constant and their relationship with microwave absorbing properties are investigated in sintered Ni-Zn ferrite. Toroid specimens of
${(Ni_{0.5}Zn_{0.5}O)}_{1-y}{(Fe_{2}O_{3})}_{1+y}$ ferrites are prepared by conventional ceramic processing technique. The large change in magnetic permeability is observed by the variation of excess$Fe_{2}O_{3}$ in the Ni-Zn ferrites. The more the iron-excess from y=0.04 to y=0.12, the lower value of both$\mu_{r}'$ and$\mu_{r}"$ is observed. However dielectric permittivity increases with the increase of the increase of the excess$Fe_{2}O_{3}$ . The control of permittivity is realized by nitrogen sintering atmosphere and excess$Fe_{2}O_{3}$ respectively. -
An experiment was carried out to investigate the effect of
$Na_{2}O$ additive on the magnetic and physical properties of$SrZn_{2}-W$ type hexagonal ferrite. The specimens were prepared by the conventional manufacturing methods without atmosphere control. It was found that the magnetic properties of SrO.2ZnO.$8Fe_{2}O_{3}$ are considerably improved on adding 1.5wt%$Na_{2}O$ . Theoptimum condition of making magnet with suitable properties are as follows : chemical analysis composition :$Sr^{2+}_{0.852}Zn^{2+}_{1.721}Na^{+}_{0.301}Fe^{2+}_{0.723}Fe^{3+}_{15.703}O_{27}$ ; semisintering condition :$1300^{\circ}C\;{\times}\;1h$ in air ; sintering condition :$1250^{\circ}C\;{\times}\;0.5h\;T_{c}=371^{\circ}C,\;H_{A}=1091.5kA/m,\;K_{A}=2.13{\times}10^{5}J/m^{3}\;and\;n_{B}=31.8\mu\textrm{B}$ . -
For the fabrication of a multi-pole anisotropic Sr-ferrite magnet by powder injection molding, it is important to control effectively the alignment of magnetic powders during the injection molding process. The effect of the fluidity of powder/binder mixture on the powder alignment was studied with changing the particle sizes and the volume fraction of Sr-ferrite magnetic powders. The critical volume fraction of Sr-ferrite powders increases from 58 vol.% to 64 vol.% as the mean powder size increases from
$0.8\;\mu\textrm{m}$ to$1.2\;\mu\textrm{m}$ . A Sr-ferrite powder alignment greater than 80 % is achieved at the conditions of an apparent viscosity lower than 1000 poise at$1600\;sec^{-1}$ shear rate, an applied magnetic field higher than 4 kOe, and a powder volume fraction 8 vol.% lower than the critical fraction. The powder alignment obtained during the injection molding process is not much affected by the subsequent processes of debinding and sintering, showing the magnetic properties of 3.8 kG of remanent flux density and 3.37 kOe of intrinsic coercivity. -
Magnetic nanoparticles of iron and iron oxide have been prepared in a modified upward thermal diffusion cloud chamber using pulsed laser evaporation. SEM/TEM studies of these particles reveal a size distribution with a mean diameter of about
$60\;{\AA}$ . FTIR spectrum measurements are used to investigate the difference in oxidation level between nanoparticles prepared at different partial oxygen pressures. The complex magnetic behaviour of these particles was studied using DC- and AC-susceptibility measurements. All samples exhibit superparamagnetism with blocking temperatures ranging from 50 K to above room temperature. The coercivity fields as well as the dependence of the blocking temperature on measuring frequency have been studied. magnetic anisotropy constants are found to be one order of magnitude higher than is known for the bulk values. The mean particle size estimated from the magnetic data is found to be in perfect agreement with the TEM observations. -
Electronic structures of the Heusler compounds, XMnSb (X=Ni, Pd, and Pt) are investigated systematically by using the linearized muffiu-tin orbital (LMTO) band method. LMTO band calculations yield that, by including the spinorbit interactions, the NiMnSb and PtMnSb are half-metallic, while PdMnSb is normal metallic at the experimental lattice constant. The effect of the spin-orbit interaction is substantial in PtMnSb, in contrast to NiMnSb and PdMnSb. The calculated X d and Mn 3d angular momentum projected local density of states's reveal that the hybridization between the Mn 3d X d states increases from X = Pt to Pd and Ni.
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Systematic studies on the crystal structure and magnetic properties of light rare earth element(RE) compounds with Pb,
$REPb_{2}$ , have been carried out. Their crystal structure has been identified to be a$MoSi_{2}$ -type. The values of the effective magnetic moment for$CePb_{2},\;PrPb_{2}\;and\;NdPb_{2}$ are respectively very close to the theoretical values of$RE^{3+}$ . These three compounds are antiferromagnetic and exhibit a metamagnetic transition. The magnitude of the Neel temperature is proportional to two-thirds of the de Gennes factor. The magnetic entropy change for$NdPb_{2}$ is contrast to the value for$CePb_{2}$ heavy-fermion compound, comparable to the theoretical value. The magnetic contribution to the temperature dependence of resistivity for$PrPb_{2}$ is given by a form of -lnT in a wide temperature range, implying the Kondo system in analogy with$Cepb_{2}$ . -
Kaneko, T.;Fujimori, H.;Yoshida, H.;Watanabe, K.;Abe, S.;Matsumoto, M.;Yoshida, T.;Kanomata, T. 758
The magnetization of$Mn_{1-x}Co_{x}Pt_{3}$ ordered alloys was measured at various temperatures and the pressure effect on$T_{c}$ for X=0.25, 0.5 and 0.6 was examined. The X dependence of$T_{c}$ determined by Arott plot has a minimum near X=0.6. The field-cooling effect measurement for X=0.5 shows a reentrant spin glass behavior. It is found that there is a concentration showing no pressure dependence of$T_{c}$ between X=0.25 and 0.5. These magnetic properties are discussed with a rigid band model. -
The coercive field
$H_{c}$ of amorphous Y-Fe alloys in the spin-glass state has been investigated. Foramorphous$Y_{10}Fe_{90}$ alloy, the thermal variations of$H_{c}$ in the maximum external field$H_{max}=300,\;600$ and 1 k Oe exhibit a maximum. Since spin-glass behavior is strongly affected by external magnetic fields, the maximum point moves to lower temperature with increasing$H_{max}$ . The appearance of the maximum in$H_{c}$ has been discussed in terms of the change of the spin-glass state in the external magnetic field. When the value of$H_{max}$ is 55 kOe, the temperature dependence of$H_{c}$ has no maximum and shows an exponential decrease with increasing temperature. Similar trends have been observed over a wide concentration range. The concentration dependence of$H_{c}$ is associated with the magnetic phase diagram. -
The atomic structure and magnetic properties of
$LaCo_{13}$ amorphous alloy have been investigated and compared with those of its crystalline counterpart. It has been confirmed that the amorphous alloy is composed of the icosahedral clusters with a$NaZn_{13}$ -type structure. The magnetic moment and the spin- wave stiffness constant obtained from the magnetic measurements in the amorphous state are larger than those in the crystalline state. The Curie temperature estimated from the reduced magnetization curve for the former is much higher than the value for the latter. The localized magnetic moment character in the amorphous state is stronger than that in the crystalline state. -
The effect of small addition of Nb on the electrical resistivity and Hall coefficient of the amorphous
$Fe_{83}Zr_{7}B_{10}$ alloy and annealed ones below the crystallization temperature were investigated, which has been considered to be suitable for high frequency core material. At room temperature, their resistivities$\rho$ and the spontaneous Hall coefficients$R_{s}$ are$~1.6\;{\mu}{\Omega}m$ and$~3{\times}10^{-8}m^{3}/As$ , respectively.$R_{s}$ and$\rho$ are decreased with increasing temperature from 100 K to room temperature. Side-jump effect was adopted to analyze the effect of the small variation of concentration and annealing. The quantity of$R_{s}/{\rho}^{2}$ at room temperature, which is directly related to the electronic structure of the mother alloy, remained almost a constant except as quenched one as it can be predicted from the side-jump effect. We suggested the temperature dependence of$R_{s}/{\rho}^{2}$ can be compared to Ms{T}. -
The mixed ferrite
$Ni_{x}Co_{1-x}Fe_{2}O_{4}$ have been investigated by X-ray and$M\"{o}ssbauer$ spectoscpy. From the results of X-ray diffraction measurement the structure for this system is spinel, and the lattice constant is in accord with Vegard's law.$M\"{o}ssbauer$ spectra of$Ni_{x}Co_{1-x}Fe_{2}O_{4}$ have been taken at various temperature ranging from 13 to 800 K. The isomer shifts indicate that the valence states of the irons at both A(tetrahedral) and B(octahedral) sithe are found to be in ferric high-spin states. The variation of magnetic hyperfine fields at the A and B sites are explained on the basis on A-B and B-B supertransferred hyperfine interactions. It is found that Debye temperatures for the A and B sites of$CoFe_{2}O_{4}$ and$NiFe_{2}O_{4}$ are found to be${\theta}_{A}=734{\pm}5K,\;{\theta}_{B}=248{\pm}5K,\;and\;{\theta}_{A}=378{\pm}5K,\;{\theta}_{B}=357{\pm}5K$ , respectively. Atomic migration of$Ni_{0.3}Co_{0.7}Fe_{2}O_{4}$ starts near 450 K and increases rapidly with increasing temperature to such a degree that 61 % of the ferric ions at the A site have moved over to the B site by 700 K. -
In this paper,
$Mn^{2+}$ ion was doped in Y-Ba-Cu-O as an EPR probe. The following samples were prepared by conventional solid-state reaction method :$YBa_{2}Cu_{2.96}Mn_{0.04}O_{7-\delta}$ (MN-I), annealed$YBa_{2}Cu_{2.96}Mn_{0.04}O_{7-\delta}$ (AMN) and$YBa_{2}Cu_{2.94}Mn_{0.06}O_{7-\delta}$ (MN-II). AMN sample was obtained from MN-I by annealing for 1 hr under the Ar gas atmosphere at$600^{\circ}C$ . X-band (~9.05 GHz) EPR spectra were measured from 103 K to room temperature by employing a JES-RE3X spectroscopy with a$TE_{0.11}$ cylindrical cavity and 100 kHz modulation frequency. In MN-I we have observed only the$Cu^{2+}$ signal. The fact that no$Mn^{2+}$ signal was observed, in spite of$Mn^{2+}$ being a very sensitive EPR probe, indicates that most likely isolated$Mn^{2+}$ ions don't exist in the MN-I sample. Most probably$Mn^{2+}$ ions in the MN-I sample interact antiferromagnetically and hence are EPR silent. The AMN spectra of at room temperature and 103 K indicate not only the$Cu^{2+}$ signal but also an extra signal, which increases with decreasing temperature. It is suggested that the extra signal originates from Mn ions that were antiferromagnetically coupled before the annealing process. In MN-II, from 103 K to room temperature, also, the extra signal was observed together with the$Cu^{2+}$ signal. The extra signal in MN-II, however, decreases with decreasing temperature and nearly disappears at 103 K. The signal originates from Mn ions in impurity phases that include$Mn^{2+}$ ions. We suppose that there exist at least two$Mn^{2+}$ doped phases in Y-Ba-Cu-O. The$Mn^{2+}$ signal of one phase is undectable at all temperature and that of another phase decreases with decreasing temperature and disappears around 103 K. -
With a newly designed capacitive torque sensor a multipurpose magnetometer for measuring basic magnetic characteristics such as hyteresis loops, magnetic anisotropy and magnetostriction was built. In order to calibrate the capacitive torque sensor, we measured the output voltages of the sensor by applying the torques due to the electromagnetic and gravitational forces. Experimental results of the several calibration method for the capacitive torque sensor showed good agreement within 3 %.
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Differential equations governing dynamic behavior of toroid-shaped ferro-magnetic material having a small gap of uniform width were derived incorporating Maxwell equations of electromagnetic induction relevent to the system and Newtonian equation of motion. Once the external uniform magnetic field was applied within the material through dc-circuit around the toroid, gap begin to change which lead to the abrupt variation of field in the material and gap according to the differential equations already derived. Characteristics of current and electromotive force with respect to time in the circuit consisting of inductance and resistance in series could be predicted from numerical solutions of these equations. As current in the circuit increasesl, magnetic field in the material increases, thus, the gap starts to shrink due to increased attractive force between gap and elastic restoring force in the material. With an appropriate selection of elastic constant of toroidal ferromagnetic material and design of gap structure it is possible to obtain the specified in both linear and nonlinear magnetic characteristics, such as current dependent and independent inductance.
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The magnetostriction versus field (
${\lambda}-H$ ) curves for the melt-spun ribbons of$Dy_{x}{(Fe_{1-y}B_{y})}_{1-x}$ (x=0.2, 0.25, 0.3; y=0, 0.05, 0.1, 0.15, 0.2) alloys are measured systematically at various wheel speeds ranging from 10 to 50 m/sec. The${\lambda}-H$ curves in most cases vary sensitively with the wheel speed and, in the wheel speed range where no amorphous phase is formed, the magnetic softness improves rather continuously with the wheel speed. This result is considered to be due to the reduced grain size with increasing wheel speed, which was confirmed by X-ray diffraction and transmission electron microscopy. In particular, homogeneous and ultrafine grains with size of about 10 nm are formed even in the as-spun state when the$Dy_{0.3}{(Fe_{1-y}B_{y})}_{0.7}$ alloys are quenched at the wheel speed of 30 m/sec (for the alloy with y=0.2) or 40 m/sec (for the alloys with$y{\leq}0.15$ ) and the ribbons having the nanocrystalline grain structure exhibit good magnetostrictive characteristics. -
The complex permeability dispersions and the microwave absorbing phenomena are investigated in ferrite microwave absorber. The complex permeability of NiZn ferrite, NiZnCo ferrite, and Y-type hexagonal ferrite were measured in 200MHz-14GHz range. Two types of resonances, the domain wall and the spin rotational resonance, were observed. With a ferrite particle with a diameter of about
$1\;\mu\textrm{m}$ , only spin rotational resonance were observed. The theoretical matching frequency is determined by plotting the measured complex permeability locus on the impedance matching solution map. One or two impedance matching phenomena are observed in the ferrite absorbers according to their complex permeability loci on the impedance matching solution map. The first matching frequency, found in the ferrite-rubber composites, which was higher than that of spin rotational resonance, increased with spin rotational resonance frequency. -
In order to widen the band-width of ferrite absorber, compositional effect on the complex permeability of Ni-Zn ferrite and the structure of grid absorber were studied. From the experimental results, we could determine the optimum composition composition of Ni-Zn ferrite and the structure of grid absorber. Also, we manufactured grid absorber and investigated its microwave absorbing characteristics. Calculation shows that the ferrite frid absorber suppresses reflection
${\leq}-20dB$ from 30 MHz to 700 MHz and the conventional ferrite tile absorber suppresses reflection${\leq}20dB$ in the frequency range of 30 MHz-400 MHz. It was found that the microwave absorbing performance of the ferrite grid absorber was superior to the ferrite tile absorber. -
LPE growth experiment were carried out to make garnet crystal for Faraday rotator and we have evaluated the characteristics of Faraday rotator by a measurement system which is consist of electromagnet and optical components, also done Laue pattern analysis. The thickness of garnet film was
$180\;\mu\textrm{m}$ and the Faraday rotation of this film was 388 deg/Cm at wavelength$1.55\;\mu\textrm{m}$ , room temperature. -
Ac susceptibility of iron-nitride magnetic fluids with various particle number densities was measured. Therelaxation time increases rapidly as the temperature decreases or the inter-particle interaction increases. The analysis of the data suggests that the activation energy is proportional to
${(k_{B}T/J_{typ})}^{\alpha}$ with$\alpha$ ~-0.24 in the lower temperature range in which the thermal energy is comparable to the magnetic dipole interaction. -
The oil-based magnetic fluids were sysnthesized using ultra-fine
$Fe_{3}O_{4}$ powder dispersed in hydrocarbon oil. To synthesize ultra-fine$Fe_{3}O_{4}$ , we carried out the experiments varying the pH of reacting medium and the initial concentration of$Fe^{2+}$ . We also investigated the amount of oleic acid to obtain a stable dispersion and the proper base oil of MF for loudspeaker application. The limits of adsorbed amount of oleic acid on the$Fe_{3}O_{4}$ surface were approximately 35~40 percents of the total magnetite weight. As the$Fe_{3}O_{4}$ content increased from 0.1g/cc to 0.6g/cc, the viscosity of oil-based magnetic fluid increased from 1,063cP to 1,828cP, and its saturation magnetization at 10kOe increased from 66G to 242G. When we tested the MF sample to a commercial speaker, improvements were noted. -
Dielectromagnets are permanent magnets made from resin-bonded hard magnetic powders. Magnetic properties of dielectromagnets depend on kind of used hard magnetic materials as chemical compound, shape, size of grain and applied technology. Comparison of advantages and disadvantages of dielectromagnets made from different kind of magnetic powders induced us to try to prepare dielectromagnets from mixture of hard magnetic powders, not only one of them. The purpose of investigation on this kind of dielectromagnets is to find formula to prepare permanent magnets with properties adequate to different kind of electrical motors requirements. As hard magnetic materials we used powders of ferrite, melt-spun ribbon Nd-Fe-B and Alnico. Papers present results of investigation on technology of this kind of dielectromagnets. It shows also influence of kind of mixture and used technology on magnetic properties of dielectromagnets.
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This paper describes the efficient design, analysis method and experimental verification of capacitor discharge impulse magnetizer system. A capacitor discharge magnetizer system is used to produce a high current impulse of short duration in this magnetizing fixture. The parasitic resistance and parasitic inductance of the capacitor discharge impulse magnetizer system have been estimated using known air-core test coil. Finite element analysis (using MAXWELL 2-D field simulator) and magnetizing circuit analysis (using SPICE) are also used as part of the design and analysis process of the capacitor discharge impulse magnetizer system. Application study for a magnetizing fixture design is shown. 8-pole magnetizing fixture has been designed and analyzed using finite element analysis. The fixture design for 8-pole magnet are presented along with the experimental results. The experimental results have been achieved using a high-voltage, high-energy capacitor discharge impulse magnetizer and 8-pole iron core fixtures (charging voltage : 2000[V], capacitor bank : 4000[
$\mu\textrm{F}$ ]). -
A capacitor discharge impulse magnetizer is used to produce a high current pulse of short duration in a magnetizing fixture for magnets of the various shapes. The problem of designing custom fixtures for magnetization has often been considered more of conventional experience than a scientific theory. Therefore, the design of magnetizingfixture has until recently been a "cut and try" process. It was common to literally blow up one or more fixtures beforeachieving the desired results. Finite element CAD package allow the design of such a fixture. Since magnetizing fixtures come in a variety of sizes and shapes, there is usually no simple analysis method that can be used to estimate the field characteristics of the fixtures. Instead, one typically uses finite element analysis. FEA program MAXWELL is the primary tool used here. The purpose of this study was a examine both theoretically and experimentally the field characteristics inside the fixture. Independent of sizes and shapes of magnetizing fixtures, the desired magnetic field can be obtained with resonable predictability. The experimental results have been achieved using a 1000[V], 22.4[KJ] capacitor discharge magnetizer and iron-core fixtures.
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Finite element analysis using two dimensional magnetic permeabillity tensor that can represents phase lag between magnetic field intensity and flux density under rotational flux is examined. Considered problem is confined to two dimensional magnetostatic case. And we applied proposed method to calculate the core loss of the test model and compare the result with that of experiment.
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The effect of small addition of Nb on the electrical resistivity and Hall coeffcient of the amorphous
$Fe_{83}Zr_{7}B_{10}$ alloy and annealed ones ones below the crystallization temperature were investigated, which has been considered to be suitable for high frequency core material. At room temperature, their resistivities$\rho$ and the spontaneous Hall coeffcients$R_{s}$ are$~1.6\;{\mu}{\Omega}m$ and$~3{\times}10^{-8}m^{3}/As$ , respectively.$R_{s}$ and$\rho$ are decreased with increasing temperature from 100 K to room temperature. Side-jump effect was adopted to analyze the effect of the small variation of conentration and annealing. The quantity of$R_{s}/{\rho}^{2}$ at room temperature, which is directly related to the electronic structure of the mother alloy, remained almost a constant except as quenched one as it can be predicted from the side-jump effect. The unexpected temperature dependence of$R_{s}/{\rho}^{2}$ measured at low fields much below Tc is left as a question. -
국소섭동을 포함하는 비대칭성 계의 전자구조 물성을 연구하기 위해서 밀접 결합 (tight-binding ; TB) linear-muffin-tin-orbital(LMTO) 방법과 회귀(recursion ; R) 방법을 결합한 실공간 전자구조 방법인 제일원리-자체충족적-스핀분극 TB-LMTO-R 방법을 개발하였다. 이 방법을 강자성 물질인 bcc Fe, hcp Co, fcc Ni등에 적용하여 송이의 크기, 회귀 계수, TB-LMTO Hamiltonian의 차수등을 변화시키며 국소 상태밀도와 자기 모멘트등의 수치적 수렴도를 고찰하였다. 송이 크기는 5,000개 원자 이상, 연속 분수 계수 n은 40이상, TB-LMTO Hamiltonian의 차수는 2차 이상이며 TB-LMTO-R 방법이 기존의 LMTO 방법의 결과와 거의 일치하는 결과를 준다는 사실을 얻었고 실공간 전자 구조 방법으로 TB-LMTO-R 방법의 충분한 신뢰도를 확인 하였다.
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비자성 분순물을 갖는
$CuF_{2}.2H_{2}O$ 의 수소 핵자기공명을 77-295 K의 온도범위에서 수행하였다. 그 결과 수소의 스핀-격자 완화율을 지배하는 메카니즘이 구리 전자 스핀의 재주넘기(filp)와 전자-포논 상호작용(Raman process)의 변조에 의한 것임을 알 수 있었다. 또한 전자 스핀 재주넘기에 대한 교환에너지$1.8(\pm0.04)$ K를 구할 수 있었다. -
$Th_{2}Zn_{17}$ 구조를 갖는$Sm_{2}Fe_{17}$ 화합물을 이용하여$250^{\circ}C$ 에서$500^{\circ}C$ 까지 16시간 질화처리를 함으로써$Sm_{2}Fe_{17}N_{x}$ 의 질화과정 및 질소함량에 따른 자기특성을 조사하였다. 질화초기에는 모든 온도구간에서 질소함량(${\Delta}W$ )이 시간($\sqrt{t}$ )에 대하여 직선적으로 증가하고, 이 관계를 이용하여 구한 질화과정의 활성화에너지, Q=102.4 kJ/mol이다.$Sm_{2}Fe_{17}N_{x}$ 의 자기특성은 질소함량에 크게 의존하며$Sm_{2}Fe_{17}N_{2.8}$ 이 최적의 자기특성을 나타내었다. 이 질화물의 포화자화, 이방성상수, 이방성자장 및 큐리온도는 각각$M_{s}=1147\;emu/cm^{3},\;K_{1}=4.6{\times}10^{7}erg/cm^{3},\;K_{2}=6.0{\times}10^{7}erg/cm^{3},\;H_{A}=290\;kOe\;및\;450^{\circ}C$ 이다. -
비정질
$Fe_{73.5}Cu_{1}Nb_{3}Si_{16.5}B_{6}$ 리본을 DSC 곡선상의 최초 발열반응 전 후의 온도인$500^{\circ}C$ 및$552^{\circ}C$ 에서 열처리하여 열처리 시간에 따른 초미립상의 생성 과정을 뫼스바우어 분광법으로 분석하였다. 열처리된 시료에 생성된 결정상은 대부분$DO_{3}Fe-Si$ 이었으며,$t-Fe_{3}B$ 로 추정되는 강자 성상도 소량 확인되었으며, 비정질상도 잔류하여 공존함을 확인하였다.$DO_{3}Fe-Si$ 내의 Si 조성 즉, Si/(Fe+Si)는$500^{\circ}C$ 60분 열처리에서 0.218 이었으며,$552^{\circ}C$ 10분 열처리에서 0.222이었다. 열처리 시간이 120분이 될 때까지 이들 두 값은 감소한 후 계속된 열처리에서 0.210으로 거의 일정하게 유지되었다. 열처리 시간 에 따른 Si 조성의 변화는 초미세자기장과 이성질체이동의 변화를 유발시킨 것으로 분석할 수 있었다. 즉, Fe-Si의 평균초미세자기장의 증가와 평균이성질체이동의 감소는 Si 조성의 증가에 기인됨을 알 수 있었다. 잔류비정질의 체적분율은 초기에 급격히 감소하여$500^{\circ}C$ 와$552^{\circ}C$ 둘 다의 열처리 온도에서 120분 이후 거의 일정해 진다. 120분 이후 Fe-Si와 잔류비정질의 체적분율의 미소한 변화에도 불구하고 잔류비 정질의 평균초미세자기장의 현저한 감소는 잔류비정질내의 Nb와 B 원소의 양의 증가에 기인된다. 결정질의 체적분율은 예측과는 달리$500^{\circ}C$ 에서 180분 열처리될 경우 81 %,$552^{\circ}C$ 에서 960분 열처리될 경우 77 % 이었다. -
고 포화자속밀도를 갖는 Fe미세결정 박막의 자기특성 및 미세구조에 미치는 첨가원소의 영향을 조사하였다. Mo 첨가 박막의 경우,
$Fe_{2}Mo$ ,$Fe_{4}N$ ,$Fe_{3-2}N$ 상의 생성으로 연자기 특성이 발현되지 않았다. Ta첨가 박막의 경우, 미세한 TaN, TaC 상이 석출하여$\alpha$ -Fe 결정립을 효과적으로 미세화 시켰으며 Fe 질화물의 생성도 억제되었다. 이에 따라 우수한 연자기 특성이 발현되었으며 FeTaN계 박막은 4000, FeTaC 박막은 2700의 높은 투자율을 나타내었다. -
B의 함유량을 6 at% 고정하고 Nd함유량을 3~5 at%로 변화시킨
$\alpha$ -Fe기 Nd-Fe-B 합금의 자기특성이 조사 되었다. 급속응고법으로 제조된$Nd_{x}{(Fe_{0.9}Co_{0.1})}_{90-x}B_{6}Nb_{3}Cu_{1}(x=\;3,\;4,\;5)$ 비정질합금은 열처리에 의하여 초미세결정립으로 결정화하며, Nd의 함유량에 따라 잔류자화 및 보자력이 변한다. x=3의 경우 최적열처리조건에서$\alpha$ -Fe(Co) 부피분율의 증가로 잔류자 화는 증가하나, 보자력은 감소한다. 그러나 Nd 함유량의 증가는$Nd_{2}{(Fe,\;Co)}_{14}B$ 부피분율의 증가로 인하여 잔류자화는 감소하나 보자력은 향상된다.$640^{\circ}C$ , 10 min 열처리조건에서$Nd_{5}{(Fe_{0.9}Co_{0.1})}_{85}B_{6}Nb_{3}Cu_{1}$ 의 결정립크기는 약 20 nm이며, 잔류자화, 보자력 및 최대에너지적 은 각각 1.35 T, 219 kA/m (2.75 kOe) 및$129\;kJ/m^{3}$ (16.2 MGOe)으로 가장 우수하다. -
로렌트 SEM을 이용하여 동적자구 모양의 관찰에 대한 검토가 50 Hz ~ 10 kHz의 주파수 범위에서 수행되었다. 동적자구 모양의 관찰은 여자주파수와 SEM의 주사주파수의 정수 배와의 사이에 미소한 차를 두고 관찰하는 방법이며, 이 관찰 방법에 따라서 시뮬레이션하여 시뮬레이션한 모양과 관찰모양을 비교 검토하였다. 또한 더욱 높은 주파수에서 동적자구 모양을 관찰하기 위해서는 SEM의 주사주파수의 안정화에 대한 필요한 것을 알았다.
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유한 요소법을 사용하여 선형 이동 자기장을 이용하는 원통형 전자기 펌프 내에서 발 생하는 전자기력을 모사할 수 있는 프로그램을 개발하였다. 이 프로그램을 사용한 수치실험을 통하여 펌프에서 발생하는 전자기력은 입력 전류의 주파수, 이송 대상 용해 금속의 성질에 의존하는 것을 알 수 있었다. 또한 최대의 전자기력을 낼 수 있는 코일 의 최적 길이가 존재하고 있으며, 그 최적 길이는 표피층 두께(skin depth)가 클 때에 는 용해 금속의 반경에 의해서 결정되며, 표피층 두께가 작을 때에는 표피층 두께에 의해서 결정된다.
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돌림힘 자력계를 이용하여 일축 이방성 자성체의 M-H 이력 곡선을 측정하는 새방법을 개발하였다. 본 방법에 의한 M-H 이력 곡선으로부터 포화 및 잔류 자기화량과 보자력을 얻을 수 있었다. 본 방법의 정확도는 자기회사 비균질한 보자력 근처의 인가 자기 마당에서도 영향받지 않았다.
$2{\times}10^{-3}$ dyn cm의 측정 감도를 갖는 돌림힘 자력계를 이용한 자기화량 측정에서$10^{-6}$ emu 이상의 고감도를 얻었다. -
전원주파수 교류자기장 내성평가을 위하여 유도코일용 대형 3-축 사각 헬름홀쯔 코일 를 설계 .center dot. 제작하였다. 제작한 사각 헬름홀쯔 코일의 코일상수및 자기장 균일도를 측정하였으며, 3축 방향의 자기장 균일도는 컴퓨터 모사에의한 값과 잘 일치하였다. 자기장 균일도부터 교류자기장 내성평가에서 요구하는 유효시험공간을 결정 하였으며, 다회의 유도코일을 사용하므로써 낮은 전류로 큰 자기장을 요구하는 단속적 교류자기장 내성평가도 수행할 수 있음을 알 수 있었다.