Search

The half-metallicity and magnetism of the (001) surfaces of superlattice were investigated by means of FLAPW (Full-potential Liniarized Augmented Plane Wave) method. We considered four types of (001) surface termination, i.e., Al(S)-, Cr(S)-, P(S)Al(S-1)- and P(S)Cr(S-1)-term systems. We found that only Cr(S)-term system maintains the half-metallicity at the surface as only this system has the calculated magnetic moment of integer number of bohr magnetons. The magnetic moment of Cr(S) atom in the system was which was increased from the bulk value by the effects of band narrowing and increased spin-splitting at the surface. The electronic density of states of the P(S) atom in the P(S)Al(S-1)-term showed very sharp surface states due to the broken bonds at the surface. We found there is still a strong p-d hybridization between the P(S) and Cr(S-1) layers in the P(S)Cr(S-1)-term which causes a considerable increase of magnetic moment of P(S) atom.

Department of Physics, Inha University, Incheon 402-751, Korea(Received 11 March 2015, Received in final form 3 April 2015, Accepted 7 April 2015)Recently, a first-principles study led to a prediction that quaternary Heusler compounds, CoFeCrZ (Z = Ga, Ge) are excellent half-metallic ferromagnets. In this study, we investigate the electronic and the magnetic properties at the (001) surfaces of CoFeCrGa andCoFeCrGe by means of the full-potential linearized augmented plane wave (FLAPW) method within generalized gradientapproximation. We considered two types of surface termination: CoFe-terminated and CrZ-terminated surfaces, Z being either Ga orGe. From the calculated total magnetic moments and the local density of states, we found that half-metallicity is not preserved for allthe surfaces. But the calculated atomic density of states showed that CrGa-terminated surface of the CoFeCrGa is almost half-metallic.The magnetic moment of the Co, Fe, or Cr atoms at the surface or subsurface layers in each system had very different values.Keywords: half-metallicity, surface magnetism, electronic structure

We investigated the half-metallicity and magnetism at the (001) and (110) surfaces of YC in zinc-blende structure by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. From the calculated local density of states, we found that neither (001) nor (110) surface preserves the half-metallicity. While the magnetic moment of Y atom in the YC bulk is 0.116 μB, it is 0.057 μB at the topmost layer of Y-terminated (001) surface. On the contrary, C-terminated (001) YC surface exhibits stronger magnetism than the bulk structure; the calculated magnetic moment on topmost C atom is 1.084 μB, while that of C atom in the bulk structure is 0.423 μB. The magnetic properties of the non-polar (110) YC surface are slightly enhanced as compared with the bulk structure.

The electronic and the magnetic properties of (001) surface of KCaN2 half-metallic compound with full-Heusler structure are studied with the use of a full-potential linearized augmented plane wave method. Two possible terminations of the surface are considered and only the one with N atoms in the topmost layer is found to retain the half-metallic properties of the bulk. The magnetic properties of N-terminated surface are enhanced compared with the properties of the bulk. The calculated magnetic moments on the N atoms in the KCaN₂ are 1.26 μB in the bulk and 1.90 μ B at the surface. The subsurface metal atoms are also slightly polarized. In the surface terminated with metal atoms, not only the half-metallicity is destroyed, but also the magnetic properties of the system are weakened.

Magnetism at the interfaces of rocksalt structured half-metals, NaN and CaN were investigated by use of the first-principles band calculations. The electronic structures for the simple interface and mixed interface systems were calculated by the FLAPW (full-potential linearized augmented plane wave) method. From the calculated number of electrons in muffin-tin spheres of each atom, we found, for the simple interface system, that the magnetic moment of the N atom in the CaN (NaN) side is increased (decreased) compared to those of inner N atoms. For the mixed interface system, the magnetic moments of the interface N atoms are similar to the averaged value for the inner N atoms in CaN and NaN side. Among four interface N atoms, the N atom connected to Na atoms in the upper and down layers has the largest magnetic moment and that connected to Ca atoms has the smallest. The number of p electrons in each N atom and the calculated density of states explain well the above situation.

Compounds such as NaN belong to an interesting class of materials in which a magnetic order may appear despite the lack of d electrons. The magnetic properties of these materials are ascribed to the partially filled p shells. Recently, on the basis of electronic structure calculations from first principles, it has been found that NaN is a ferromagnetic half-metal in rocksalt (RS) and zinc-blende (ZB) structures with half-metallic band gaps in majority electron channels. The former structure has appeared to be more stable. From the first-principles calculation, we found that the half-metallic properties of the bulk RS and ZB NaN are conserved at the RS(001) and ZB(110) surfaces. Due to the interactions between Na s and N p electrons, N atoms become positively polarized. In the RS NaN (001) the calculated values of the magnetic moments of the N atoms is about . The magnetic moment on the N atom in the top most layer of ZB(110) is slightly larger than that of the RS(001) surface, i.e., . The Na atoms in the both structure are hardly polarized.

암염구조를 가진 SiTe에서 일부 Si를 Cr로 치환한 화합물에 대한 전자구조와 자성을 교환상관퍼텔셜에 일반기울기 근사를 쓴 full potential linearized augmented plane wave 에너지 띠 계산방법을 이용하여 연구하였다. Si 대신 25 %의 Cr을 치환한 CrSi₃Te₄ 및 50 %를 치환한 CrSiTe₂를 고려하였다. 총에너지 계산으로 CrSi₃Te₄는 11.64 a.u, CrSiTe₂는 a = 7.89 a.u., c = 11.13 a.u.의 평형격자상수를 가짐을 알았다. CrSiTe₂는 단위부피당 정수인 4 μB의 자기모멘트를 가지는 반쪽금속성을 나타냈으며, CrSi₃Te₄는 단위부피당 자기모멘트가 4 μB보다 미세하게 컸다. 두 화합물 모두에서 치환되어 들어간 Cr은 3.6 μB 정도의 자기모멘트를 가졌으며, Si나 Te는 약하게 자기화되었다. 계산된 스핀분극 상태밀도를 이용하여 이 두 화합물의 자성을 논의하였다.

We investigated the magnetism of vanadium monolayers on a Pd(001) surface. The electronic structure and the magnetic properties of the V/Pd(001) system were determined with the use of the full-potential linearized augmented plane-wave method within the general gradient approximation. Three magnetic configurations were studied: non-, ferro-, and antiferromagnetic. From the total energy calculations, we found that the V/Pd(001) system is the most stable in the antiferromagnetic configuration. The importance of relaxation on the magnetic properties of the systems was also studied. It was found that the Pd(001) surface covered with a V monolayer undergoes considerable relaxation in which the spacing between Pd layers increases in all three magnetic configurations. Contrary to the Pd interlayer spacing, the distance between the V overlayer and the topmost Pd layer is reduced. The interlayer spacing between the V overlayer and the Pd surface layer is the largest for the antiferromagnetic configuration. In the relaxed antiferromagnetic structure, the magnitude of the calculated magnetic moments on the V atoms was 1.31 μ B . The presence of the vanadium monolayer does not affect the paramagnetic properties of the Pd(001) surface.

상관효과 U가 전자구조와 자성에 미치는 영향을 검토하기 위하여 대표적 자성물질인 철의 덩어리, 단층 및 사슬 구조에 대해 연구하였다. 이를 위하여 U = 3 eV로 택하여, 총 퍼텐셜 보강 평면파동 에너지 띠 방법을 이용하여 LDA+U 및 GGA+U 근사 하에 전자구조 계산을 수행하였다. 비교를 위하여 LDA 및 GGA를 이용한 계산도 수행하였다. 그 결과 U의 효과를 포함시켰을 때 덩어리 철의 경우 자기모멘트가 0.3 μ B 증가하여 실험값이나 LDA 및 GGA 계산에 비해 과다하게 계산되는 것으로 나타났으나, 단층이나 사슬의 경우는 그렇게 큰 차이를 보이지 않았다. 이로부터 전자구조 계산 시 대상 계에 따라 U의 효과를 적절히 고려하여야 함을 알았다.

In order to investigate the origin of the band gap in the half-metallic Heusler alloy, , through the electronic structure calculation, we have calculated the electronic structures for the compounds consisted of parts of Heusler structures, i.e. zinc-blende CoMn, half-Heusler CoMnSi, and artificial , using the full-potential first-principles band calculation method. By investigating the band hybridization and energy gap for the calculated density of states for these compounds, we found that the the origin of the band gap is not consistent with the explanation discussed by Galanakis et al. We have also discussed the magnetism for these compounds by the calculated number of majority- and minority-spin electrons.

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 μ B 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.

The electronic structure and magnetism of superlattice systems consisted of Heusler compound (CMS) and zinc-blende MnAs (MA) are investigated by means of the all-electron full potential linearized augmented plane wave method within the generalized gradient approximation. Four superlattice systems are considered, that is CMS(m)/MA(n), where m and n, being either 2 or 4, denote the number of alternatingly arrayed layers of the compounds in a superlattice along [001] direction. From the calculated total magnetic moments as well as the total density of states, it is found that neither of the four systems is half-metallic. It is also found that the Mn atoms are antiferromagnetically coupled in the systems of CMS2/MA2 and CMS2/MA4. The total and atom-resolved density of states of the four superlattices are compared with those of the bulk and MnAs, and the influences of the change in the systems symmetry on the magnetism and half-metallicity are discussed.

We calculated the electronic structures of substituted cobalt nitrides, that is and , by using the all electron fullpotential linearized augmented plane-wave (FLAPW) energy band method, and investigated the influence on the magnetic properties of due to the substitution of Co atom located at corner sites by iron and nickel atoms. We found that the magnetic moments of CoII atoms located at the face-center positions in these compounds are almost same to that of . The magnetic moments of Fe and Ni atoms in and are 3.086 and , and they have the localized nature of magnetism.

We investigated the electronic structure and magnetic properties of zinc-blende CrP/SrBi interface by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. It is found that the half-metallicity is destroyed when the two half-metals are in contact. Magnetic moments of the atoms forming the supercell differ considerably from the respective values obtained for the bulk structures of the two materials. Cr atoms being and not being in contact with Bi atoms have magnetic moment 3.43 and 2.69 μ B , respectively. Bi atoms lose their majority electrons which results in their negative polarization. Alkaline Sr atoms are very weakly negatively polarized. The spin distribution within the supercell is such that well separated regions of positive and negative polarization are seen, especially around the layer of P atoms being in contact with the layer of Sr atoms.

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 μ B ) in the CrGa-Term and the surface Co (1.17 μ B ) in the Co-Term were much increased compared to those of the inner-layers (1.79 and 0.77 μ B ), respectively, while that of the subsurface Cr atom in the Co-Term was decreased to 1.19 μ B .

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 μ B . 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.

We investigated the magnetic properties of VRu(001) surface by using the all electron full-potenial linearized augmented planewave (FLAPW) energy band method within the GGA. We consider two different configurations, V and Ru surface layers, respectively. The V atoms in surface layer was calculated to have large magnetic moment of while the Ru surface layer to have nearly nonmagnetic state. The calculated spin-polarized density of states. spin density contour, and charge density were discussed in relation to the magnetic properties of VRu(001) surface.

We investigated the electronic structures and the magnetic properties of Ti based intermetallic system of CoTi/FeTi/CoTi(110) surface and interface by using the all-electron full potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). The calculated magnetic moments of interface Co and Fe atoms are 0.65 and 0.15 μ_B, respectively. Surface and interface magnetism of CoTi/FeTi/CoTi(110) are discussed using the calculated density of states (DOS) and the spin densities.

The electronic structures and magnetism of MgCCo(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, 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 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.

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.