• Journal of the Korean Magnetics Society
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• v.7 no.3
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• pp.146-151
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• 1997

Buffer (t $\AA$)/ CoFe(35$\AA$)/Cu (50$\AA$)/Co (35$\AA$) sandwiches prepared by dc magnetron sputtering on Corning glass substrates using the $Co_{90}Fe_{10}$ and Co layers with different coercivities. Dependence of magnetoresistance on the type and thickness of buffer layers, and on the thickness of Cu and the magnetic layers in buffer/ CoFe/Cu /Co sandwiches were investigated. Magnetoresistance ratio and saturation field $H_s$ increased as thickness of the buffer layer becomes thicker, then decreased smoothly after a maximum value. An improved filed sensitivity was realized with the $Ni_{81}Fe_{19}$ buffer layer.

• Journal of the Korean Magnetics Society
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• v.14 no.5
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• pp.163-168
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• 2004

We prepared ultra thin film structure of Si(100)/ $SiO_2$(200 nm)/Ta(5 nm)/Ni$_{80}$Fe$_{20/(l～15 nm)}$Ta(5 nm) using an inductively coupled plasma(ICP) helicon sputter. Magnetic properties and cross-sectional microstructures were investigated with a superconduction quantum interference device(SQUID) and a transmission electron microscope(TEM), respectively. We report that NiFe films of sub-3 nm thickness show the B$_{bulk}$ = 0 and B$_{surf}$=-3 ${\times}$ 10$^{-7}$(J/$m^2$). Moreover, Curie temperature may be lowered by decreasing thickness. Coercivity become larger as temperature decreased with 0.5 nm - thick Ta/NiFe interface intermixing. Our result implies that effective magnetic properties of magnetoelastic anisotropy, saturation magnetization, and coercivity may change abruptly in nano-thick films. Thus we should consider those abrupt changes in designing nano-devices such as MRAM applications.

• Journal of the Korean Magnetics Society
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• v.10 no.2
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• pp.49-52
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• 2000

The changes of magnetic properties in neutron irradiated F $e_{81}$ $B_{13.5}$S $i_{3.5}$ $C_2$ amorphous ribbon were studied by X-ray diffraction, hysteresis loop, temperature dependence of magnetization and complex permeability. The fluences of thermal ( $n_{th}$) and fast ( $n_{f}$) neutron were 6.95$\times$10$^{18}$ $n_{th}$ c $m^{-2}$ and 4.56$\times$10$^{16}$ $n_{f}$c $m^{-2}$ , respectively. The changes of XRD Profiles were not observable at the neutron irradiated sample. The complex permeability spectra showed that the permeability from domain wall motion decreased due to the increase of pinning force against domain motion by the neutron irradiation, and the relaxation frequency of rotational magnetization moved to higher frequency region. The measurement of hysteresis loop showed the increase of magnetic softness, related to rotational magnetization, but saturation magnetization was decreased in neutron irradiation sample. The Curie temperature was decreased in the neutron irradiated sample.e.e.e.

• Journal of the Korean Magnetics Society
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• v.8 no.1
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• pp.34-41
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• 1998

We have theoretically investigated torque curve shapes of simple uniaxial magnetic materials by considering conditions for round peaks to exist. These conditions are functions of an applied field, anisotropy field, ans lowest critical field $h_0$ for a domain wall to move or nucleate. The peak having a height of 2h appears when h is lower than h$_1$, the peak having a height of 1 appears when h is higher than h$_2$, ans two peaks having heights of 1 and -1 appear when h is higher than h$_3$. It was found that torque curves of simple uniaxial magnetic materials could be classified into 8 distinct types depending on the existence of hysteresis, the number of the round peaks, and the reversal mechanisms. Simple uniaxial magnetic materials also found to be classifed into the 5 groups depending on $h_0$.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.438-444
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• 2000

The prediction of mechanical properties for WC-Co alloys by evaluation of coercive force and magnetic saturation were studied in relation to their microstructure. The WC-8%Co alloys were prepared using different WC particle size, carbon content and various sintering temperature by PM process. The magnetic properties such as coercive force and magnetic saturation of sintered WC-Co alloys were critically dependent upon their final composition and microstructure. Slight changes of carbon contents and small variation of WC grain size result in marked changes of magnetic properties, hardness and transverse rupture strength of sintered WC-Co alloys. It was found that the coercive force and hardness were increased by fine WC grain size of sinterd alloys, and the coercive force was proportional to hardness. With decreasing total carbon content below the stoichiometric value in WC-8%Co alloys the volume fraction of $\eta$ phase increased steadily, while the magnetic saturation and transverse rupture strength decreased. The magnetic saturation was inversely proportional to the coercive force of WC-Co alloys.

• Journal of the Korean Magnetics Society
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• v.4 no.4
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• pp.313-318
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• 1994

We have investigated the effects of deposition angle on magnetic and magneto-optic properties in Co/Pt multilayer thin films. which were prepared bye-beam evaporation on tilted substrates. with varying tilt angle from $0^{\circ}$ to $60^{\circ}$. The structure of the specimens was examined by x-ray diffractometer and scanning electron microscope. and the magnetic and magneto-optical properties were measured by VSM, torque magnetometer, and Kerr loop tracer. X-ray diffractometry revealed that all of the specimens had multilayer structure and growth orientation of column followed the tangent rule but the crystallograpic orientation, <111>, was slightly deviated from the substrate normal even though the deposition angle was increased up to $60^{\circ}$. A decrement of the magnetization and Kerr angle with the deposition angle was related with that of the film density due to increasing porosity. The perpendicular mag¬netic anisotropy was also decreased with increasing the deposition angle.

• Journal of the Korean Magnetics Society
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• v.2 no.2
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• pp.119-124
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• 1992

We have investigated the effects of sputtering Ar gas pressure on magnetic and magneto-optical properties in compositionally modulated Co/Pd superlattice thin films. The samples were prepared by dc magnetron sputtering from 2-in.-diam Co and Pd targets by alternately exposing the substrates to targets. Sputtering Ar gas pressure was varied from 2 to 30 mTorr. All samples had same bilayer thicknesses composed of 2-$\AA$-thick Co and 9-$\AA$-thick Pd sublayers. It was observed that the colum-nar structure was more distinctively developed with increasing Ar gas pressure. We observed that the intrinsic uniaxial anisotropy energy, magnetization and polar Kerr rotation were decreased with increasing Ar gas pressures. Large coercivity and perfect squareness were attained by the deposition at the high Ar gas pressure. We believe that the results are mainly ascribed the variation of micro-structure with sputtering Ar gas pressure.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.55-59
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• 1991

The temperature-dependent magnetization curves of amorphous Fe-Co-(Nd, Sm, Gd, Tb)-B alloys were measured using a vibrating sample magnetometer from 77 K up to 900 K. The spin wave stiffness constants and the range of the exchange interaction were calculated from the saturation magnetization values at 0 K. Curie temperatures and the Bloch coefficients estimated from the saturation magnetization curves. The low temperature dependence of magnetization is in good agreement with Bloch relation, $M_{s}(T)=M_{s}(O)(1-BT^{3/2}-CT^{5/2})$. The spin wave stiffness constant and the range of exchange interaction are decreased by substitution of heavy rare earth (Tb, Gd).

• Journal of the Korean Magnetics Society
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• v.3 no.3
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• pp.196-200
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• 1993

$(Sm_{0.5}RE_{0.5})Fe_{11}Ti$ compounds have tetragonal $ThMn_{12}$-type structure and show the uniaxial magnetocrystalline anisotropy with the easy magnetization c-axis. Among the $(Sm_{0.5}RE_{0.5})Fe_{11}Ti$ series, RE=Sm shows the highest anisotropy field of 11200 kA/m(140 kOe). On the other hand, RE=Nd has the highest saturation magnetization of $122.3\;Am^{2}/kg$(122.3 emu/g) and RE=Gd the highest Curie temperature of $326^{\circ}C$.

• Journal of the Korean Magnetics Society
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• v.4 no.2
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• pp.114-121
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• 1994

A $Ba_{2}Co_{2-x}Zn_{x}Fe_{12}O_{22}(x\;=\;0.0~2.0,\;Co_{2-x}Zn_{x}Y)$ powder was prepared by a oxidation--coprecipitation method and sintered at $1150~1250^{\circ}C$ for 4 hours. The microstructures and magnetic properties(saturation magnetization, Curie temperature), complex permeability of sintered body were measured As increasing Zn content from x = 0 to 2.0 in $Co_{2-x}Zn_{x}Y$, the real value of complex permeased from 7 GHz to 1 GHz. Because of resonance in few GHz range, Y-type hexagonal ferrite is rmre applicalble than spinel ferrite in high frequency range, and more research would be necessary to find the mechanism of the second resonance observed in higher frequency.