• Journal of Magnetics
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• 제11권1호
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• pp.8-11
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• 2006

Recently half-metallic full-Heusler alloy films have attracted significant interests for spintronics devices. As these alloys have been known to have a high spin polarization, very large TMR ratio is expected in magnetic tunnel junctions. Among these alloys, $Co_2MnSi$ full-Heusler alloy with a high spin polarization and a high Curie temperature is considered a good candidate as an electrode material for spintronic devices. In this study, the magnetic and structural properties of $Co_2MnSi$ Heusler alloy films were investigated. TMR characteristics of magnetic tunnel junctions with a $Co_2MnSi/SiO_2/CoFe$ structure were studied. A maximum MR ratio of 39% with $SiO_2$ substrates and 27% with MgO(100) substrates were obtained. The lower MR ratio than expectation is considered due to off-stoichiometry and atomic disorder of $Co_2MnSi$ electrode together with oxidation of the electrode layer.

• Journal of Magnetics
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• 제13권4호
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• pp.115-119
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• 2008

The authors predicted that $Co_2HfSi$, a $Co_2$-based full Heusler alloy, is being a half-metallic ferromagnet by first-principles calculations using the all electron full-potential linearized augmented plane wave method which adopts the generalized gradient approximation. The integer value of the calculated total magnetic moment of 2.00 ${\mu}_B$ per formula unit and a spin gap of 0.69 eV in spin down state confirmed the half-metallicity of bulk $Co_2HfSi$. For the $Co_2HfSi$(001) surface, we considered two possible surface terminations, namely, Co terminated and HfSi terminated surfaces. It was found that half-metallicity was retained at the HfSi-terminated surface but not at the Co-terminated surface. The magnetic moment of surface Co atoms in the Co-terminated surface was slightly lower than that of Co atoms in deep inner-layers, whereas the magnetic moments of Hf and Si atoms at the HfSi-terminated surface were almost same as those in deep inner-layers.

• 한국자기학회지
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• 제18권6호
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• pp.201-205
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• 2008

호이슬러 구조의 대표적 반쪽금속인, $Co_2MnSi$에서 에너지 간격이 생기는 원인을 실제적인 전자구조 계산을 통해 검토하기 위해 호이슬러 구조에서 부분을 이루는 zinc-blende 구조의 CoMn과 하프 호이슬러 구조를 가진 CoMnSi, 그리고 가상적인 화합물인 $Co_2Mn$의 전자구조를 제일원리 방법을 통해 계산하였다. 각 화합물에서 계산된 상태밀도를 이용하여 띠 혼성이나 에너지 간격 등을 고찰한 결과 $Co_2MnSi$에서 에너지 간격이 생기는 원인이 Galanakis 등이 설명한 방식이 그대로 적용되지 않았으며, Si 원자의 역할 또한 중요함을 알게 되었다. 각 화합물에서 얻은 다수스핀과 소수스핀 전자수를 통해 이들 화합물의 자성도 고찰하였다.

• Journal of Magnetics
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• 제12권3호
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• pp.97-102
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• 2007

We have investigated the electronic structures and magnetism of a full Heusler alloy $Co_2CrGa(001)$ surface by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). We considered two types of different terminations: the Co-terminated (Co-Term) and the CrGa-terminated (CrGa-Term) surfaces. From the calculated layer-projected density of states (LDOS), we found that the surface of the CrGa-Term shows nearly half-metallic character while that of the Co-Term is far from the half-metallic. For the Co-Term, the surface Co atom moves down to the bulk region by $0.05{\AA}A$, while the subsurface Cr and Ga atoms move up to the surface layer by 0.05 and $0.01{\AA}$, respectively. For the CrGa-Term, there is a large inward relaxation of the surface Ga atom $(0.07{\AA})$, but the relaxation of the surface Cr atom is very small $(0.01{\AA})$. The relaxations affect not much to the overall shapes of DOS for both terminations, but make the surface states of the surface Cr and Ga atoms for the CrGa-Term shift to higher energy that enhances the nearly half-metallic character of the CrGa-Term. The magnetic moments of the surface $Cr(2.98{\mu}_B)$ in the CrGa-Term and the surface $Co(1.17{\mu}_B)$ in the Co-Term were much increased compared to those of the inner-layers $(1.79\;and\;0.77{\mu}_B)$, respectively, while that of the subsurface Cr atom in the Co-Term was decreased to $1.19{\mu}_B$.

• 한국자기학회지
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• 제26권6호
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• pp.185-189
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• 2016

이 연구에서는 방사광을 이용한 연 X-선 흡수 분광법(soft X-ray absorption spectroscopy: XAS)과 광전자 분광법(photoemission spectroscopy: PES) 을 이용하여 반쪽금속 반강자성체 후보 물질인 $Mn_3Ga$ 호이슬러 화합물의 전자구조를 연구하였다. 이 연구에 사용된 시료는 full-Heusler $Mn_3Ga$로 ball milling 후 열처리하지 않은 시료와 ball milling 후 $400^{\circ}C$에서 열처리한 두 시료를 사용하였다. XAS 분석에 의하면 $Mn_3Ga$에서 Mn 이온들의 원자가는 $Mn^{2+}$ 상태임을 알 수 있었으며, 국소적으로 팔면체 대칭성을 가진 Mn 이온들과 사면체 대칭성을 가진 Mn 이온들이 섞여 있음을 알 수 있었다. 그리고 $Mn_3Ga$의 가전자띠 PES 스펙트럼은 전자구조 계산에 의한 반쪽 금속성 상태밀도와 대체로 유사함을 발견하였다.