M Shimizu

Electronic structure and magnetic properties of Y-Ni intermetallic compounds

The local density of states at Ni and Y sites and the total density of states are calculated for the intermetallic compounds Y2Ni17, YNi5, Y2Ni7 and YNi3 in the recursion method. It is shown that the occurrence of ferromagnetism in Y2Ni17, Y2Ni7 and YNi3 is due to a peak in the density of states near the Fermi level. The temperature dependence of the spin paramagnetic susceptibility is calculated and the results are compared with the observed ones. The metamagnetism in Y2Ni16 and some local magnetic properties on Ni and Y atoms are discussed.

Electronic structure and magnetic properties of Y-Co, Y-Fe and Y-Mn intermetallic compounds

Electronic densities of states in Y-Co (Y2Co17, YCo5, Y2Co7 and YCo3), Y-Fe (Y2Fe17, Y6Fe23 and YFe3) and Y6Mn23 intermetallic compounds are calculated in the tight-binding d-band model by making use of the recursion method. The average and local magnetic moments on Co and Fe atoms, the high-field susceptibility and the coefficient of the low-temperature specific heat are calculated and compared with the experimental values. The temperature dependences of the spin susceptibility and the spontaneous volume magnetostriction in Y-Fe compounds are also calculated and compared with the experimental results.

Electronic structure and magnetic properties of Y2Fe14B

Electronic density of states (DOS) in Y2Fe14B is calculated by the recursion method. The total DOS is similar to that in Y2Fe17. The values of the low-temperature specific-heat coefficient, the local; magnetic moment on non-equivalent Fe sites and the high-field spin susceptibility at 0K and the temperature variation of the paramagnetic spin susceptibility are calculated and compared with the experimental results. It is shown that there is a relationship between the magnitude of the local magnetic moments and the average nearest neighbour distance between Fe atoms and that the local magnetic moment on the 4c site of Fe atoms is strongly field dependent.

Calculation of the anisotropic magnetoelastic coupling constants in iron

Formulae for the anisotropic magnetoelastic coupling constants B1 and B2 related to shear strains in itinerant electron ferromagnets with cubic symmetry are derived by the perturbation theory where a tight-binding parametrisation scheme for the electron-ion and spin-orbit couplings is used. Numerical computations of B1 and B2 are carried out for iron. The results are compared with the empirical values estimated by the phenomenological theory and the agreement between them is satisfactory for B1 but not for B2. The discrepancy is discussed.

Pressure effect on the Curie temperature in dilute ferromagnetic alloys

The pressure dependence of the Curie temperature dTC/dP in dilute transition metal alloys and rare earth Co2 compounds is calculated in the combined model of localised spins and itinerant d electrons. It is found that dTC/dP varies as -TC at low TC and this result agrees qualitatively with many experimental results in dilute transition metal alloys. The calculated values of d ln TC/d ln V for Pd-Fe, Pd-Co, Pd-Ni, Pt-Fe and Pt-Co alloys and for the GdCo2 compound are compared with the experimental results. The calculated values of d ln TC/d ln V for Pd-Fe alloys agree well with the experimental values, which show a maximum at about 60K. The calculated results predict that there also exists a maximum in the experimental values of d ln TC/d ln V for (Gd-Y)Co2 compounds and Pd-Co alloys.

Electronic structure and magnetic properties of amorphous YCo2

The electronic density of states of amorphous YCo2 is calculated in the tight-binding d-band model. The atomic structure is constructed by a dense random packing of hard spheres relaxed by the Morse potential. The effects of hybridisation of the d bands between Y and Co, of the local environment of each atom and of the distance between Y atoms on the electronic structure are studied, and it is found that the local-environment effect is the most significant. By making use of the value of the molecular field coefficient in crystalline YCo2, it is found that amorphous YCo2 becomes ferromagnetic. The magnetic moment on a Co atom, the low-temperature specific heat coefficient and the high-field spin susceptibility are calculated and compared with the experimental results.

Pressure dependence of the spin susceptibility in vanadium

Pressure dependence of the spin susceptibility chi spin in vanadium is calculated within the framework of the local spin density approximation. It is found that the change in chi spin due to pressure is mainly caused by the change in the density of states at the Fermi level; the contribution from the change in the exchange-correlation integral is very small. The calculated result is compared with experiment by using a simplified model for the volume dependence of the orbital susceptibility.

A calculation of magnetic properties of Fe3Pt alloys

Densities of states of disordered and ordered ferromagnetic Fe3Pt alloys are calculated in the tight-binding d-band model with intra-atomic Coulomb interaction by making use of the coherent potential approximation for disordered alloys and the recursion method for ordered alloys. Magnetic properties such as the magnetisation, local magnetic moments low-temperature specific heat coefficient and spontaneous volume striction are calculated and compared with experiment. It is found that both the ordered and disordered Fe3Pt alloys are strong ferromagnets and that the ground-state properties can be explained by the Hartree-Fock approximation.

A phenomenological theory of magnetoelasticity in itinerant electron ferromagnetism

The contributions to the ultrasonic sound velocities or the elastic constants and the high-field susceptibility due to the magnetoelastic coupling and their anisotropies in cubic itinerant electron ferromagnets are calculated. The anisotropic spontaneous and forced magnetostrictions and the magnetoelastic contributions to the compressibility are also calculated. From the thermodynamic relations among these quantities which are tensors the enhancement due to the magnetoelastic coupling in the compressibility, high-field susceptibility and forced magnetostriction is obtained. It is shown that the experimental results on the magnetoelastic contributions to the ultrasonic sound velocities or the elastic constants and on the magnetostrictions are consistent with each other in Ni and the values of the magnetoelastic coupling constants are estimated. The present theory is also applied to Fe-Ni and Fe-Pt Invar alloys.

Effects of strain on orbital magnetic and spin paramagnetic susceptibilities in metals

Linear dependence on strain of the orbital magnetic and spin paramagnetic susceptibility tensors for Bloch electrons in metals are derived. The results are applied to a metal with cubic symmetry before deformation. An anisotropic orbital magnetic susceptibility tensor and a paramagnetostriction tensor as well as spin contribution are obtained for a deformed crystal. The orbital and spin contribution to the volume paramagnetostriction are calculated for a single crystal and those contributions to the volume dependence of the total magnetic susceptibility for a polycrystalline sample are also given.