Setsuro Asano

Band Theory of Antiferromagnetic Chromium

The band structures of Cr in the paramagnetic- and the perfect antiferromagnetic state are evaluated by the Greens function method. In the former the crystal potential is set up by the self-consistent procedure proposed by Wakoh, while the alternant orbital theory of Slater is applied to the latter. The spin-dependent part of the potential is determined by the Slater exchange with an adjustable parameter which is determined so as to give an observable value of the magnetic moment. The Fermi surfaces of both the states are calculated. The induced magnetic moment, the electronic specific heat and the magnetic form factor are also evaluated. The agreement between theory and experiment seems to be satisfactory. The stability of the perfect antiferromagnetic state against the paramagnetic state is discussed on the basis of the effective Hamiltonian. Finally, the stability of the spin-density-wave state in Cr is ascribed to the special band structure of Cr.

Theoretical search for half-metalliic films of Co2MnZ (Z Si, Ge)

Abstract To search a half-metallic (HM) film, we calculated the energy band structures of the films of Co 2 MnZ (Z  Si, Ge) which were theoretically predicted to be HM in the bulk. The band structures of the (0 0 1) and (1 1 1) films show that whether the film becomes HM or not is conditional on its thickness and its surface and that the (1 1 1) film with the Z atom surface is appropriate as a FM film.

A Half-Metallic Band Structure and Fe2MnZ (Z=Al, Si, P)

Band calculation results show that Heusler compounds Fe 2 MnZ (Z=Al,Si,P) have a band gap near the Fermi energy for one spin direction. Except for Fe 2 MnSi, the compounds does not have a half-metallic character because there is a slight density of states at the Fermi energy in the minority-spin state. An analysis of density of states indicates that there exists sufficiently strong d - d hybridization between metal atoms and weak p - d hybridization between Si and metal atoms. Due to this weakness, the replacement of Si by Al or P does not cause considerable change in the DOS structure. However, the weak hybridization defines the electronic character of the system.

Electronic Structure and Lattice Transformation in Ni2MnGa and Co2NbSn

It is known experimentally that Heusler alloys, Ni 2 MnGa and Co 2 NbSn undergo the cubic-to-tetragonal lattice transformation, in a ferromagnetic state and a paramagnetic one, respectively. We calculated electronic structures of Co 2 NbSn and Ni 2 MnGa for both cubic and tetragonal structures by KKR method. Comparing the density-of-state of the cubic and tetragonal structures for each alloy, it is expected that the band Jahn-Teller effect cause the lattice transformation in both alloys.

Electronic Structure of CsCl-Type Transition Metal Alloys

Transition metal alloys have a tendency to make a stable ordered lattice of the CsCl-type, when the average number of conduction electrons (including d-electrons) is the same as that of Cr. The electronic structures of VMn, TiFe and ScCo are investigated by the self-consistent KKR method, to clarify the stability of these alloys. It is found that the density-of-states of these alloys has a deep valley in the middle region, by which bonding and antibonding orbitals are well separated, and the Fermi energy lies in the valley. The electronic structure of ordered alloy ScCu is also investigated. Here the narrow d-bands of Cu are situated well below the d-bands of Sc, and s-, p-electrons are polarized by about 0.6/atom at the Cu-cell. Thus, the ionic bond seems to be important to make a stable ordered lattice of ScCu. § I. Introduction

Band Theory of Antiferromagnetism in 3d f.c.c. Transition Metals

The band structure of both paramagnetic and antiferromagnetic γMn is evaluated by G.F.M. with the Slater exchange approximation. The observed magnetic moment (2.3µ B ) is self-consistently obtainable, if the full Slater exchange is reduced by about one-half. The situation is the same at Cr. No special charactors are observed in E ( k )-curves of γMn contrary to the case of Cr. Introducing a simple exchange interaction term - J eff δ n 2 by the random phase approximation, we extend Muellers interpolation scheme to apply to the antiferromegnetic case, and antiferromagnetism in f.c.c. structure is examined within the limit of the rigid band rigid band approximation. If we assume the value J eff =0.060Ry, f.c.c. Mn and f.c.c. Fe are antiferromagnetic and their magnetic moments are determined as 2.3µ B and 0.7µ B , respectively, which are in good agreement with experimental values. In f.c.c. structure the gap mechanism similar to Cr is found to be effective around N ≈7.3. The theoretical prediction seems to b...

Magnetic and half-metallic properties of new Heusler alloys Ru2MnZ (Z Si, Ge, Sn and Sb)

Abstract Electronic structures of new Heusler alloys Ru 2 MnZ (Z  Si, Ge, Sn and Sb) were calculated to examine the magnetic properties. In this paper, it will be shown that an antiferromagnetic state is stable for these alloys, where the Mn magnetic moments are aligned ferromagnetically in the (111) plane and antiparallel along the [111] direction. It will also be shown that the alloys Ru 2 MnZ (Z  Si, Sb) can be half-metallic in a ferromagnetic phase.

Electronic Structures and Magnetic Properties of the C14 Laves Phase Compounds ZrMn2, TiFe2 and NbFe2

The electronic structures were calculated by the KKR and the local-spin-density methods for ZrMn 2 , TiFe 2 and NbFe 2 . The densites-of-states (DOSs) of the C14 Laves phase compounds AB 2 are characterized by the DOSs of the atoms B(2a) and B(6h) around the Fermi level which play an important role in investigating their magnetism. We can guess from the structures of the DOSs and the number of valence electrons whether or not a compound is magnetic.

Theoretical Study on the Magnetocrystalline Anisotropy of X/Co (X=Pd, Pt, Cu, Ag, Au) Multilayers

The magnetocrystalline anisotropy energies of X(2ML)/Co(1ML) (ML: monolayer) (X=Pd, Pt, Cu, Ag, Au) multilayers have been calculated from first principles within the local-spin-density approximation using the linear muffin-tin orbitals method. The easy axis of Pd/Co, Pt/Co and Au/Co are found to be perpendicular to the film plane, which are in good agreement with experiments.

Bandstructures and Hyperfine Fields of Heusler Alloys

The bandstructures were calculated by the local-spin-density (LSD) method for the alloys Cu 2 MnAl, Ni 2 MnSn, Pd 2 MnSn, Pd 2 MnSb, Co 2 MnSn, Co 2 TiSn, Co 2 TiAl and Mn 2 VAl. We calculated the magnetic moments and the hyperfine fields for these alloys on the basis of the bandstructures. The peak near the Fermi level of the density-of-states (DOS) curve is characteristic for Co in Co 2 YZ and plays an important role in determining the magnetic moment and the hyperfine field. For Mn 2 VAl, the magnetic moments on Mn and V are antiparallel. Roughly speaking, the calculated hyperfine fields are in good agreement with the experimental ones. However, we evaluate the contribution to the hyperfine field from inner core s -electrons small when we use the LSD method.