• Journal of Magnetics
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• 제3권4호
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• pp.105-111
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• 1998

The low energy excitations of spin waves (SWR) in thin films can be used for determination of the surface anisotropy constant and the nonhomogeneities of magnetization in the close-to-surface layer. The dispersion relation in SWR is sensitive on the geometry of experiment. We report on temperature dependence of surface magnetic anisotropy energy constant in magnetic semiconductor thin films of$ CdCr_{2-2x}In_{2x}Se_4$ at spin glass state. Samples were deposited by rf sputtering technique on Corning glass substrate in controlled temperature conditions. Coexistence of the infinite ferromagnetic network (IFN) and finite spin slusters (FSC) in spin glass state (SG) is know phenomena. Some behavior typical for long range magnetic ordering is expected in samples at SG state. The spin wave resonance experiment (microwave spectrometer at X-band) with excited surface modes was applied to describe the energy state of surface spins. We determined the surface magnetic anisotropy energy constant versus temperature using the surface inhomogeneities model of magnetic thin films. It was found that two components contribute to the surface magnetic anisotropy energy. One originates from the exchange interaction term due to the lack of translation symmetry for surface spin as well as from the originates from the exchange interaction term due to the lack of translation symmetry for surface spin as well as from the stray field of the surface roughness. The second one comes from the demagnetizing field of close-to surface layer with grad M. Both term linearly decrease when temperature is increased from 5 to 123 K, but dominant contribution is from the first component.

• 한국자기학회지
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• 제21권1호
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• pp.1-4
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• 2011

정육면체 전이금속 산화물 FeO, MnO의 자기적 상호작용을 제1원리의 범밀도함수법을 이용하여 계산하였다. 그 결과, 모두 초교환작용으로 인해 반강자성적 상호작용이 가장 낮은 에너지를 가지고 있었다. 자기이방성은 반강자성 스핀 배열의 FeO 클러스터에서만 발견되었다. 그 원인은 <111> 방향으로 각운동량을 가지는 3d down-spin 전자의 스핀-궤도 결합에 기인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.61-61
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• 2011

Using ab initio calculations, we study the MgO(001) and Fe/MgO(001) surface phases and the effects of interface structure on the Fe/MgO magnetic anisotropy. The surface phase diagrams of MgO(001) and Fe/MgO(001) show that the most stable surface structures are either defect-free surface or the surfaces with oxygen vacancies in c($2{\times}1$) periodicity for the systems. By the formations of the oxygen vacancy rows on MgO(001) surface, the in-plane magnetic anisotropy energy of Fe overlayer is reduced while the perpendicular magnetic anisotropy energy is increased from 0.1 to 0.5 meV per Fe atom.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2012년도 자성 및 자성재료 국제학술대회
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• pp.104-105
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• 2012

The temperature dependence of the effective magnetic anisotropy constant K(T) of ferrite nanoparticles is obtained based on the measurements of SQUID magnetometry. For this end, a very simple but intuitive and direct method for determining the temperature dependence of anisotropy constant K(T) in nanoparticles is introduced in this study. The anisotropy constant at a given temperature is determined by associating the particle size distribution f(r) with the anisotropy energy barrier distribution $f_A(T)$. In order to estimate the particle size distribution f(r), the first quadrant part of the hysteresis loop is fitted to the classical Langevin function weight-averaged with the log?normal distribution, slightly modified from the original Chantrell's distribution function. In order to get an anisotropy energy barrier distribution $f_A(T)$, the temperature dependence of magnetization decay $M_{TD}$ of the sample is measured. For this measurement, the sample is cooled from room temperature to 5 K in a magnetic field of 100 G. Then the applied field is turned off and the remanent magnetization is measured on stepwise increasing the temperature. And the energy barrier distribution $f_A(T)$ is obtained by differentiating the magnetization decay curve at any temperature. It decreases with increasing temperature and finally vanishes when all the particles in the sample are unblocked. As a next step, a relation between r and $T_B$ is determined from the particle size distribution f(r) and the anisotropy energy barrier distribution $f_A(T)$. Under the simple assumption that the superparamagnetic fraction of cumulative area in particle size distribution at a temperature is equal to the fraction of anisotropy energy barrier overcome at that temperature in the anisotropy energy barrier distribution, we can get a relation between r and $T_B$, from which the temperature dependence of the magnetic anisotropy constant was determined, as is represented in the inset of Fig. 1. Substituting the values of r and $T_B$ into the $N{\acute{e}}el$-Arrhenius equation with the attempt time fixed to $10^{-9}s$ and measuring time being 100 s which is suitable for conventional magnetic measurement, the anisotropy constant K(T) is estimated as a function of temperature (Fig. 1). As an example, the resultant effective magnetic anisotropy constant K(T) of manganese ferrite decreases with increasing temperature from $8.5{\times}10^4J/m^3$ at 5 K to $0.35{\times}10^4J/m^3$ at 125 K. The reported value for K in the literatures is $0.25{\times}10^4J/m^3$. The anisotropy constant at low temperature region is far more than one order of magnitude larger than that at 125 K, indicative of the effects of inter?particle interaction, which is more pronounced for smaller particles.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.356.2-356.2
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• 2014

Spin Transfer Torque (STT) is of great interest in data writing scheme for the Magneto-resistive Random Access Memory (MRAM) using Magnetic Tunnel Junction (MTJ). Scalability for high density memory requires ferromagnetic electrodes having the perpendicular magnetic easy axis. We investigated CoZr as the ferromagnetic electrode. It is observed that interfacial magnetic anisotropy is preferred perpendicular to the plane with thickness dependence on the interfaces with Pt layer. The anisotropy energy (Ku) with thickness dependence shows a change of magnetic-easy-axis direction from perpendicular to in-plane around 1.2 nm of CoZr. The interfacial anisotropy (Ki) as the directly related parameters to switching and thermal stability, are estimated as $1.64erg/cm^2$ from CoZr/Pt multilayered system.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2016년도 자성 및 자성재료 국제학술대회
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• pp.155-155
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• 2016

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.314-314
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• 2011

Using first principles calculations, we investigated the interface structure effects on the magnetic properties of the Fe/BaTiO3 system. On the BaO-terminated surface, a Fe monolayer is formed as two Fe atoms are adsorbed on the top sites of Ba and O in the ($1{\times}1$) surface unit and a Fe ML is formed on the TiO2-terminated surface as two Fe atoms are adsorbed on the two O top sites. The magnetic anisotropy energy of Fe was higher on the TiO2?-erminated surface (1.5 eV) than on the BaO-terminated surface (0.5 eV). The decomposed electron density of the states showed that the stronger hybridization of Fe with the TiO2 layer than with the BaO layer is the most important reason for the higher magnetic anisotropy energy.

• 한국자기학회지
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• 제1권2호
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• pp.42-48
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• 1991

대표적인 철계비정질 합금인 $Fe_{80}B_{15}Si_{5}$의 기초연자기특성을 펄스법으로 측정하였다. 자기변형, 이방성에너지, 자화율의 역수들 사이의 정량적 관계를 연구하였다. 자기변형과 일축이방성에너지의 자화율의 역수에 대한 상대적인 기여도를 계산하였다. 내부응력의 크기와 듀도이방성에너지를 추산하였다. 시료의 장축방향으로 인가된 장력은 유도 이방성에너지를 크게 증가하게 함을 알았다.

• 한국자기학회지
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• 제8권5호
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• pp.261-269
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• 1998

스퍼터링 중 500~600 Oe의 자기장을 인가한 상태에서 제조된 비정징 Sm-Fe 합금 박막에서 6$\times$104 J/m3 크기의 유도자기이방성이 형성되었다. 자장 증착에 이해유도자기이방성이 형성된 합금 박막은 이방성이 형성되지 않은 합금 박막에 비해 자구 구조에 무관한 "포화" 자기변형은 유사하지만, 측정 방향에 따른 자기변형의 이방성 비는 최대 35 정도로서 매우 크게 증가하였다. 이는 자기변형 박막의 디바이스 응용시 성능을 크게 향상시키므로, 실용적인 측면에서 매우 중요하다. 스퍼터링 중 자기장을 인가하지 않고 통상의 마그네트론 스퍼터링에 의해 제조된 비정질 Sm-Fe 합금 박막을 넓은 조성 범위에 걸쳐서 체계적으로 소자한 결과, 이러한 합금 박막에서도 미약하나마 스퍼터링 중의 누설 자계에 의해 증착 도중 유도자기이방성이 형성되는 것을 관찰하였으며, 최대의 유도자기이방성은 Sm 함량 25~30 원자%에서 얻어졌다. 또한 본 합금 박막의 유도자기이방성은 자장 중 열처리에 의해서도 형성되는 것을 관찰하였는데, 형성된 이방성의 크기는 자장 증착에 의해 제조된 시료보다 매우 작게 나타났다. 이는 자장 증착의 경우 원자의 표면 확산을 통한 원자의 이동에 의해 유도자기이방성이 형성되나, 증착 후 자장 열처리에 의한 경우는 체적 확산에 의해 유도자기이방성이 형성되기 때문으로 생각된다.때문으로 생각된다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 C
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• pp.1295-1297
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• 1994

At 34 at% Co-Fe, the aluminum anodic oxidized (alumite) films of particle diameter $150{\AA}$ have large perpendicular anisotropy energy and high coercive force. However, for the samples of particle diameter larger than $450{\AA}$, the bottom of each particle forms abnormal part called branch-shaped different from that of particle diameter $150{\AA}$. In this case the magnetic anisotropy energy Ku was about zero at the compositions of 45 and 75 at% Co. Furthermore, at tile compositions from 50 to 70 at% Co, the values of Ku became negative value. We confirmed that Fe-C deposited the bottom of particle orients very strongly and it has a large influence upon the magnetic anisotropy energy.