Orbital Magnetic Moment in Superlattices of Transition Metals

抄録

The spin (M_s) and orbital magnetic moments (M_o) of a Co atom are calculated for various superlattices of Co atoms in fcc Pd or Cu matrix on the basis of the tight-binding model including s, p and d orbits, where the intraatomic multipole interaction between d electrons is taken into account with the Hartree-Fock approximation. A test calculation for pure Fe, Co and Ni with use of parameters obtained by fitting with the first-principles calculation shows that the method well describes the ratio M_o/M_s. Two types of enhancement of M_o of the Co atom in superlattices are proposed based on a semi-quantitative calculation with assuming ferromagnetism. In the Pd matrix, the enhancement is shown to arise from the increase of the lattice parameter, which causes the narrowing of 3d density of states; the atomic environment of a Co atom in the matrix, i.e., the numbers of neighboring Co or Pd atoms are the minor effect. In the Cu matrix, on the other hand, the difference in the effective hybridization in the 3d state between Co-Co and Co-Cu pairs mainly determines the extent of the narrowing of Co 3d states and therefore the extent of the enhancement. If all the nearest neighbors of a Co atom are occupied by Cu atoms, it is shown that M_o can be comparable to M_s.