Comparative studies of electronic and magnetic structures in Y2Fe14B, Nd2Fe14B, Y2Co14B, and Nd2Co14B

Abstract

The electronic structures of ${\mathrm{Y}}_2$ ${\mathrm{Fe}}_{14}$B, ${\mathrm{Nd}}_2$ ${\mathrm{Fe}}_{14}$B, ${\mathrm{Y}}_2$ ${\mathrm{Co}}_{14}$B, and ${\mathrm{Nd}}_2$ ${\mathrm{Co}}_{14}$B are calculated using the first-principles orthogonalized linear combinations of atomic orbitals method including spin polarization. Results are presented for total density of states (DOS) as well as spin-projected, orbital-projected, and site-projected partial DOS’s. Different transition-metal–transition-metal and transition-metal–rare-earth interactions have resulted in slightly different electronic structures for the four crystals. The Y-Fe interaction is found to be substantially stronger than the Y-Co interaction. The spin magnetic moments at each of the six inequivalent transition-metal sites are evaluated and found to be in good agreement with neutron-scattering data. The site-decomposed spin magnetic moments are sensitive to the location of the structures in the majority- and the minority-spin bands with respect to the Fermi level. The charge density and the spin density on the basal plane, the (110) plane, and a special plane containing e, $k_1$, and B sites are calculated from the eigenfunctions and plotted in the form of contour maps. The B atom is found to form strong multicenter bonds within the trigonal prism which are responsible for stabilizing the tetragonal unit cell. The spin density in the (110) plane shows an infinite array of a network type of structure which could be related to its superior permanent magnetic properties. Comparison with other relevant experimental data and possible extension of the present work are also discussed.