Junji Ishida

Band theory of Co2MnSn, Co2TiSn and Co2TiAl

The electronic structures of the Heusler alloys Co2MnSn, Co2TiSn and Co2TiAl are calculated using the SAPW method. The common properties and characteristics of these three alloys are seen in their band structures. Whether or not the orbital angular momentum is quenched in the three alloys is discussed on the basis of the band structures. For the Co atom in the Co2MnSn, Co2TiSn and Co2TiAl alloys, the orbital angular momentum is expected to contribute to the magnetic moment and the internal magnetic field.

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.

Band Theory of Super-Lattice Fe3Al

The energy bands of an ordered alloy Fe 3 Al both in paramagnetic and ferromagnetic state are calculated by the symmetrized augmented plane wave (SAPW) method. There are two types of iron atoms (Fe(I) and Fe(II)) in ferromagnetic state with a different value of the magnetic moment. The density-of-states of Fe(I) which has eight iron atoms as its nearest neighbors is different from that of Fe(II) which is surrounded by four iron atoms and four aluminum atoms. The former density is quite similar to that of iron metal, but the latter is considerably different. The d -bands of majority spin electrons mostly lie below the Fermi level, whereas those of minority spin electrons are extended across the Fermi level. The values of magnetic moments calculated for Fe(I) and Fe(II) are in good agreement with experimental values. The difference between magnetic moments on the atom Fe(II) and on Fe atom in iron metal seems to be attributed to the change of the density-of-states near the top of the d -bands. It is evident...

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.

Electronic structures and magnetic properties of T2P (T=Mn, Fe, Ni)

The electronic structures of T2P (T=Mn, Fe, Ni) which have two types of T atoms TI and TII, were calculated by the KKR and the LMTO methods in the framework of the LSD approximation. From the position of the Fermi level in the paramagnetic DOS, one can roughly guess that Mn2P exhibits antiferromagnetism, Fe2P ferromagnetism and Ni2P paramagnetism and that the magnetic moment is smaller on TI than on TII in T2P. The existence of the very sharp and high peak of DOS at the Fermi level suggests that the magnetic properties of Fe2P are sensitive to the experimental conditions. Electrons transfer from the P and TII atoms to TI atoms.

Electronic Structures of YMn2Ge2, LaMn2Ge2 and LaCo2Ge2

The electronic structures of YMn 2 Ge 2 , LaMn 2 Ge 2 and LaCo 2 Ge 2 were calculated by the KKR method in the framework of the LSD approximation. The electronic structures of the three compounds are similar and in these structures we can see the characteristics of the s , p and d bands of the constituent atoms for ThCr 2 Si 2 type compounds. Using these electronic structures, we can roughly guess the magnetism of other compounds by the rigid-band-model; YMn 2 Si 2 , LaMn 2 Si 2 , and LaCo 2 Si 2 are an antiferromagnet, a ferromagnet and a paramagnet, respectively. We find also that it is very delicate whether or not the Fe in RFe 2 X 2 (R=Y, La and X=Si, Ge) carries a magnetic moment, as indicated by the experimental results.

Electronic Structures of the Ferromagnetic Heusler Alloys

In order to see the characteristic properties of the ferromagnetic Heusler alloys,the electronic structures of Ni 2 MnSn and Pd 2 MnSn have been calculated. The common properties of these alloys have been discussed by the present results and those obtained for Cu 2 MnAl. The spin polarizations of the constituent atoms are in good are in good agreement with experimental ones. The sigmas of the spin polarizations of the s -type conduction electrons in the inscribed spheres are consistent with the signs of the measured internal magnetic fields due to the conduction electrons.

Band Calculation of Cu2MnAl

The energy bands of an ordered alloy Cu 2 MnAl are calculated by the symmetrized augmented plane wave (SAPW) method. The E ( k ) curves and the densities-of-states curves are obtained. For up-spin (minority) electrons, the density-of-states curve has two peaks. They are separated by a wide low density region in which the Fermi level is situated. The upper peak arises from the d -bands of Mn and the other one from those of Cu. On the other hand, for down-spin (majority) electrons, the state-density curves of d -bands of Cu and Mn have two peaks respectively and they are overlapped with each other. Those bands are almost occupied. The main carrier of the magnetic moment is Mn atom. The magnetic moment of the alloy has been estimated to be 3.73 µ B per molecule, which is in agreement with the measured values 3.6–4.12 µ B .

Electronic structures of the C14 Laves phase compounds AFe2 (A=Mo, Hf, Ta, W)

The band structures of AFe 2 (A=Mo, Hf, Ta, W) were calculated to examine the influence of the atom A on the electronic structures and the magnetic properties. The band structures are essentially unaffected by the difference in the kind of d bands of the atom A. The hybridization between d states of A and Fe becomes stronger with increasing the number of valence electrons of the atom A and affects the DOS curves of Fe(2 a ) and Fe(6 h ) around the Fermi level which are closely related with the magnetic properties for the C14 compounds. However, since the variation of the electronic structure with the change of the atom A is not so drastic, we can roughly guess the magnetic properties of the C14 compounds with the rigid-band-model.

Orbital angular momentum in Co2MnSn

The tight-binding orthogonalised plane-wave (TB OPW) method is used to reproduce the band structures obtained by the SAPW method. The spin-orbit interaction is treated by perturbation theory to calculate the orbital angular momentum of Heusler alloys Co2YZ on the basis of the band structures. The contributions of the orbital angular momentum to the magnetic moment on Co in Cp2YZ are 0.1, 0.07 and 0.025 mu B for Co2MnSn, Co2TiSn and Co2TiAl respectively.