J Inoue

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.

First- and second-order magnetic phase transitions in (R-Y)Co2 and R(Co-Al)2 (R=heavy rare-earth element) compounds

The types of magnetic phase transitions (first- or second-order) in (R-Y)Co2 and RCo2 (R=heavy rare-earth element) under high pressure are studied by making use of a phenomenological model where the coexistence of localised moments on R atoms and itinerant d electrons is assumed. The concentration dependence of the Curie temperature TC of R(Co-Al)2 is calculated in the same model. The calculated results of the boundary between the first- and second-order transitions are consistent with the observed results for (Er-Y)Co2 and (Ho-Y)Co2. The calculated values of TC for R(Co-Al)2 agree well with the experimental ones.

Thermal spontaneous ferromagnetism in Y2Ni7 intermetallic compound

By making use of the calculated results of the density of states, it is shown that the magnetic properties of Y2Ni7, especially the thermal spontaneous ferromagnetism, can be qualitatively explained by the simple band model. It is also shown that this conclusion is not changed by taking the effect of spin fluctuations into account.

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 Y9Co7 intermetallic compound

The local and total densities of states for the arrangement of Co atoms on the 2b sites in Y9Co7 and the local density of states for excess Co atoms on Y sites are calculated by a recursion method. All the calculated values of the local density of states on all sites at the Fermi level are not large. When the positions of Co atoms on the 2b sites are shifted a little, the adjacent Co atoms on these sites, as well as the excess Co atoms on Y sites, have a larger value of the local density of states at the Fermi level than all other sites and are capable of sustaining a local magnetic moment, or the weak ferromagnetism of Y9Co7. The paramagnetic susceptibility for Y9Co7 is calculated with two models each of which assumes excess Co atoms on Y sites and a 2b sub-band with strongly enhanced spin susceptibility.

Electronic structure and magnetic properties of Y2Co14B intermediate compound

Density of states of Y2Co14B and local density of states of Y and Co atoms are calculated by making use of the tight-binding d-band model and by the recursion method. Local magnetic moments on Co atoms are calculated from the calculated local density of states.

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.

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.