• Korean Journal of Materials Research
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• v.24 no.10
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• pp.515-519
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• 2014

The aim of this paper is to consider the effect of annealing on the coefficient of thermal expansion (CTE) of electroplated Invar Fe-Ni alloy. The CTE of the as-electroplated alloy is lower than those of alloys annealed at $400^{\circ}C$ and $800^{\circ}C$. XRD peaks become sharper as the as-electroplated alloy is annealed, which means the grain growth. The average grain sizes of as-electroplated and as-annealed alloys at $400^{\circ}C$ and $800^{\circ}C$ are 10 nm, 70 nm, and $2{\mu}m$, respectively, as determined by TEM and EBSD analyses. The CTE variation for the various grain sizes after annealing may come from the magnetostriction effect, which generates strain due to changes in the magnetization state of the alloys. The thermal expansion coefficient is considered to be affected by nano grain size in electroplated Fe-Ni Invar alloys. As grain size decreases, ferromagnetic forces might change to paramagnetic forces. The effect of lattice vibration damping of nano grain boundaries could lead to the decrease of CTE.

• Korean Journal of Materials Research
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• v.11 no.10
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• pp.859-862
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• 2001

The crystal structure and magnetic properties of the $Ni_{1-x} Cd_xFeAlO_4$(0$\leq$x$\leq$0.5) have been investigated by means of X-ray diffractometry and Mossbauer spectroscopy. The samples($0\leq$x$\leq$0.5) have been prepared by the ceramic sintering method. The X-ray diffraction pattern shows that the crystal structure of the samples is a cubic spinel type. The lattice constant has been found by extrapolation using the Nelson- Riley function and it increases slightly from $8.321{\AA}$ to $8.410{\AA}$ with Cd concentration. The Mossbauer spectra for x<0.4 show a superposition of two sextets and a paramagnetic doublet at room temperature. The cation distribution for x=0 was determined to be $[Fe_{0.75}Al_{0.25}]^A[NiFe_{0.25}Al_{0.75}^BO_4$. The superparamagnetic doublet for x< 0.4 seems to be due to A1 ion in tetrahedral site by the superparamagnetic clustering effect.

• Korean Journal of Materials Research
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• v.26 no.11
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• pp.623-627
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• 2016

$La_{1-x}Ba_xMnO_3$ (x = 0.30, 0.35 and 0.40) samples have been prepared by solid-state reaction method. The X-ray diffraction (XRD) study showed that all the samples crystallized in a rhombohedral structure with an R-3c space group. Variation of the magnetization as a function of the temperature and applied magnetic field was carried out. All the samples revealed ferromagnetic to paramagnetic (FM-PM) phase transition at the Curie temperature $T_C{\sim}342K$. The magnetic entropy change was also studied through examination of the measured magnetic isotherms M(H, T) near $T_C$. The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change. The maximum entropy change reaches a value of 1.192 J/kgK under a magnetic field change of 2.5T for the $La_{0.6}Ba_{0.4}MnO_3$ composition. The relative cooling power (RCP) is 79.31 J/kg for the same applied magnetic field.

• Korean Journal of Materials Research
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• v.15 no.6
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• pp.393-398
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• 2005

The crystal structure and magnetic properties of the $Mg_{1-x}Zn_xFeAlO_4\;(0{\leq}x\leq1.0)$ have been investigated by means of x-ray diffractometry and $M\ddot{o}ssbauer$ spectroscopy. The samples$(0{\leq}x\leq1.0)$ have been prepared by the ceramic sintering method. The x-ray diffraction pattern shows that the crystal structure of the samples is a cubic spinel type. The lattice constant has been found by extrapolation using the Nelson-Riley function and it increases slightly from $8.3496\AA\;to\;8.4128\AA$ with Zn concentration. The $M\ddot{o}ssbauer$ spectra for x<0.4 show a superposition of two sextets ana a paramagnetic doublet at room temperature. The superparamagnetic doublet for x<0.4 seems to be due to Al ion in tetrahedral site by the superparamagnetic clustering effect.

• Macromolecular Research
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• v.11 no.5
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• pp.352-356
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• 2003

The objectives of this study were to investigate the influence of gamma irradiation for sterilization on poly(D,L-lactide-co-glycolide) (PLGA) with different molecular weight and the effect of gamma irradiation on the release behavior of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU, carmustine) from PLGA wafer with various irradiation doses. The effect of gamma irradiation on PLGA was evaluated by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and electron paramagnetic resonance (EPR). The weight average molecular weight (M$_{w}$) and glass transition temperature (T$_{g}$) of PLGA decreased after gamma irradiation. The extent of M$_{w}$ reduction was dependent on irradiation dose and PLGA molecular weight. Using EPR spectroscopy, we successfully detected gamma irradiation induced free radicals in PLGA. The gamma irradiation increased the release rate of BCNU from PLGA wafer at applied irradiation doses except 2.5 Mrad of irradiation dose in this study.study.

• Current Applied Physics
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• v.18 no.11
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• pp.1289-1293
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• 2018

The influence of crystallization treatment on the structure, magnetic properties and magnetocaloric effect of $Gd_{71}Ni_{29}$ melt-spun ribbons has been investigated in detail. Annealing of the melt-spun samples at 610 K for 30 min, a majority phase with a $Fe_3C$-type orthorhombic structure (space group, Pnma) and a minority phase with a CrB-type orthorhombic structure (space group, Cmcm) were obtained in the amorphous matrix. The amorphous melt-spun ribbons undergo a second-order ferromagnetic to paramagnetic phase transition at 122 K. For the annealed samples, two magnetic phase transitions caused by amorphous matrix and $Gd_3Ni$ phases occur at 82 and 100 K, respectively. The maximum magnetic entropy change $(-{\Delta}S_M)^{max}$ is $9.0J/(kg{\cdot}K)$ (5T) at 122 K for the melt-spun ribbons. The values of $(-{\Delta}S_M)^{max}$ in annealed ribbons are 1.0 and $5.7J/(kg{\cdot}K)$, corresponding to the two adjacent magnetic transitions.

• Journal of the Mineralogical Society of Korea
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• v.31 no.4
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• pp.295-306
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• 2018

Despite the utility of solid-state NMR, NMR studies of iron-bearing silicate glasses remain a challenge because the variations in the peak position and width with increasing iron content reflect both paramagnetic effect and iron-induced structural changes. Therefore, it is essential to elucidate the effect of temperature on the NMR signal for iron-bearing silicate glasses. Here, we report the $^{29}Si$ and $^{27}Al$ MAS NMR spectra for $(Mg_{0.95}Fe_{0.05})SiO_3$ and $Fe_2O_3$-bearing $CaAl_2Si_2O_8$ (anorthite) glasses with varying spinning speed to interpret the NMR spectra for iron-bearing silicate glasses. The increase in the spinning speed results in an increase in the sample temperature. The current NMR results allow us to understand the origins of the changes in NMR signal with increasing iron content and to provide information on the dipolar interaction between nuclear spins. The $^{29}Si$ NMR spectra for $(Mg_{0.95}Fe_{0.05})SiO_3$ glass and $^{27}Al$ NMR spectra for $Fe_2O_3$-bearing $CaAl_2Si_2O_8$ glasses show that the peak shape and position of iron-bearing glasses do not change with increasing spinning speed up to 30 kHz. These results suggest that the NMR signal in the Fe-bearing glasses may stem from the 'survived nuclear spins' beyond the cutoff radius from the Fe, not from the paramagnetic shift. Based on the current results, the observed apparent shifts toward lower frequency of Al peak for $Fe_2O_3$-bearing $CaAl_2Si_2O_8$ glasses with increasing $Fe_2O_3$ at all spinning speed (15 kHz to 30 kHz) indicate the increase in the fraction of ${Q^4}_{Al}$(nSi) with lower n (i.e., 1 or 2) with increasing $Fe_2O_3$ and the spatial proximity between Fe and ${Q^4}_{Al}$(nSi) with higher n (i.e., 3 or 4). The present results show that changes in the NMR signal for iron-bearing silicate glasses reflect the actual iron-induced structural changes. Thus, it is clear that the applications of solid-state NMR for iron-bearing silicate glasses hold strong promise for unraveling the atomic structure of natural silicate glasses.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.1
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• pp.11-17
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• 2007

The spherical NiZn ferrite particles were prepared by ultrasonic spray pyrolysis with mixed solution of aqueous metal nitrates. The NiZn ferrite particle was observed with nano-sized primary particles of about 10 nm or less before annealing which represented as paramagnetic behavior measured at 77 K and room temperature. The typical abnormal growth of primary particles like polyhedral primary particles was observed by annealing at 1273 K with Zn-concentration dependency. The XRD patterns showed good crystallinity of NiZn ferrite powder after annealing. In annealing process, the intra-particle sintering phenomenon was observed and the spherical particle morphology was collapsed at 1673 K. The saturation magnetization of NiZn ferrite powder for each annealing temperature was decreased with measuring temperature of $77{\sim}$300K.

• Journal of the Korean Magnetic Resonance Society
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• v.12 no.2
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• pp.103-110
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• 2008

Spin Hamiltonian for the paramagnetic center with a three-fold symmetry and high spin ($S{\geq}2$) multiplicity should contain the fourth order zero-field splitting (ZFS) terms. Electron magnetic resonance transition lines of the center with S = 5/2 are expected to split in a pair when the magnetic field is applied off the principal axes of ZFS, while they are superimposed when the magnetic field is applied parallel to the principal axes of ZFS. In this study we report that the transition lines of $Mn^{2+}$ centers at the three-fold symmetric sites in $LiNbO_3$, chemically equivalent but physically different, split in two due to the nonzero fourth order ZFS term.

• Journal of the Korean Magnetic Resonance Society
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• v.5 no.1
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• pp.13-18
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• 2001

Natural alpha radiation produced a stable defect center to certain minerals. Electron Paramagnetic Resonance(EPR) spectroscopy is a powerful tool f3r quantifying this defect center. EPR method has been applied to trace alpha-radiation effect around the uranium ore deposit. The results show that EPR technique can be used to measure rapidly and nondestructively the defect center produced by natural alpha radiation. In general, a good correlation was achieved between defect center concentration and actinide elements(U, Th). These results imply that the concentration of defect center is dependent on the alpha radiation dose over long time scale.