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Half-metallicity and magnetism at Heusler alloy surfaces: Co<sub>2</sub>MSi(001) (M = Ti, Cr)
Jin, Ying Jiu,Lee, Jae Il WILEY-VCH Verlag 2008 Physica status solidi. PSS. A, Applications and ma Vol.205 No.8
<P>We investigated the electronic structures, magnetism, and half-metallicity at the (001) surfaces of full-Heusler alloys, Co<SUB>2</SUB>MSi (M = Ti, Cr), by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. Both the Co-terminated (Co-term) and the MSi-terminated (MSi-term) surfaces were considered. From the calculated atom-resolved density of states, we found that the half-metallicity was destroyed at the Co-term surfaces for both alloys. The electronic structures at the MSi-term surfaces of the two alloys showed much different behavior. The half-metallicity was retained at the TiSi-term for Co<SUB>2</SUB>TiSi(001) but the minority spin gap was much reduced due to surface states located just below the Fermi level. On the other hand the half-metallicity was destroyed at the CrSi-term of Co<SUB>2</SUB>CrSi(001) due to the surface states located at the Fermi level. The calculated magnetic moment of the surface Co atom of the Co-term for Co<SUB>2</SUB>CrSi(001) was increased slightly to 1.05μ<SUB>B</SUB> with respect to that of the deep inner layers (∼1.00μ<SUB>B</SUB>), while that for Co<SUB>2</SUB>TiSi(001) was decreased to 0.88μ<SUB>B</SUB>. Large enhancement of the magnetic moment was found for the surface Ti atoms at TiSi-term of Co<SUB>2</SUB>TiSi(001) and Cr atoms at CrSi-term of Co<SUB>2</SUB>CrSi(001) with values of 0.07μ<SUB>B</SUB> and 2.91(<SUB>B</SUB>, respectively. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>
Electronic Structures and Magnetism of the MgCFe₃(001) Surface
Ying Jiu Jin,I. G. Kim,J. I. Lee 한국자기학회 2002 Journal of Magnetics Vol.7 No.4
The electronic structures and magnetism of the non-oxide perovskite MgCFe₃(001) surface were investigated by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). We considered both of the MgFe terminated (MgFe-Term) and the CFe terminated (CFe-Term) surfaces. We found that the minority spin d-bands of Fe(S) of the MgFe-Term are strongly localized and Fermi level (E_F) lies just below the sharp peak of the minority spin d-band of Fe(S), while the minority spin d-bands of Fe(S) of the CFe-Term are not localized much and Fermi level (E_F) lies in the middle of two peaks of the minority spins. The majority Fe(S) d-band width of MgFe-Term is narrower than that of the CFe-Term. It is found that the magnetic moment of Fe(S) of the MgFe-Term is 2.51 μ_B, which is much larger than that of 1.97 μ_B of the CFe-Term.
Ying Jiu Jin,Jae Il Lee 한국자기학회 2007 Journal of Magnetics Vol.12 No.3
We have investigated the electronic structures and magnetism of a full Heusler alloy Co₂CrGa(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 A, while the subsurface Cr and Ga atoms move up to the surface layer by 0.05 and 0.01 A, respectively. For the CrGa-Term, there is a large inward relaxation of the surface Ga atom (0.07 A), but the relaxation of the surface Cr atom is very small (0.01 A). 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 μB) in the CrGa-Term and the surface Co (1.17 μB) in the Co-Term were much increased compared to those of the inner-layers (1.79 and 0.77 μB), respectively, while that of the subsurface Cr atom in the Co-Term was decreased to 1.19 μB.
The Electronic Structures and Magnetism of Monolayer Fe on CuGaSe₂(001)
Ying Jiu Jin,Jae Il Lee 한국자기학회 2007 Journal of Magnetics Vol.12 No.2
Ferromagnet/Semiconductor heterostructures have attracted much attention because of their potential applications in spintronic devices. We investigated the electronic structures and magnetism of monolayer Fe on CuGaSe₂(001) by using the all-electron full-potential linearized augmented plane-wave method within a generalized gradient approximation. We considered the monolayer Fe deposited on both the CuGa atoms terminated (CuGa-Term) and the Se atom terminated (Se-Term) surfaces of CuGaSe₂(001). The calculated magnetic moment of the Fe atom on the CuGa-Term was about 2.90 μB. Those of the Fe atoms on the Se-Term were in the range of 2.85-2.98 μB. The different magnetic behaviors of the Fe atoms on two different surfaces were discussed using the calculated layer-projected density of states.
Ying Jiu Jin,Jae Il Lee 한국자기학회 2008 Journal of Magnetics Vol.13 No.4
The authors predicted that Co₂HfSi, a Co₂-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 μB per formula unit and a spin gap of 0.69 eV in spin down state confirmed the half-metallicity of bulk Co₂HfSi. For the Co₂HfSi(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.
Ying Jiu Jin,Jae Il Lee 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.I
We calculated the electronic structures of several Co$_2$-based full Heusler compounds with $4d$ transition elements \textit{T} and Si, Co$_2$\textit{T}Si (\textit{T} = Y, Zr and Nb), by using the all electron full potential band method and found that the Co$_2$ZrSi is half-metallic ferromagnet. The calculated atomic resolved density of states (DOSs) for Co$_2$ZrSi showed that it had a considerably large minority spin gap ($0.94\;\text{eV}$) and that the Fermi level was pinned just at the middle of the gap. The fact that the Co$_2$ZrSi had an integer value for the magnetic moment, $2.000\;\mu_{\text{B}}$ per formula unit (f.u.), also indicated that this compound was half-metallic. Calculations for the compounds Co$_2$YSi and Co$_2$NbSi showed that they were not half-metals, but ferromagneic metals with magnetic moments of $1.002$ and $2.243\;\mu_{\text{B}}$/f.u., respectively. The Fermi level of Co$_2$YSi, located at the left edge of the minority spin gap, made the material nearly half-metallic while that of Co$_2$NbSi was positioned just below a large peak of minority Co $3d$ states.
김영구(Ying Jiu Jin),이재일(Jae Il Lee) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.3
The electronic structures and magnetism of MgCCo₃(001) surface terminated by the plane with the MgCo-Term (Mg, Co terminated) and the CCo- Term (C, Co terminated) were investigated using the all-electron full-potential linearized augmented plane-wave method. For the MgCo-Term, the magnetic moment of Co atom of the surface is strongly enhanced to 1.00 μ_B, while the magnetic moment of Co atom of the subsurface is similar to that of the center layers. For the CCo-Term, the magnetic moments of Co atoms are enhanced to 0.75 and 0.80 μ_B for the surface and subsurface layers, respectively. The magnetic moments of C and Mg atoms are coupled antiferromagnetically to that of the neighbour Co atoms. From the calculated density of states, we see that the enhancements of magnetic moments of Co atoms are closely related to localization of the Co-3d states.