Theoretical study of the magnetism within Gd/Mo and Gd/W multilayers

Abstract

The local-spin-density approximation (LSDA) and generalized-gradient approximation of Perdew, Burke, and Ernzerhof (PBE) are implemented within the framework of the semirelativistic self-consistent tight-binding linear-muffin-tin orbital in the atomic-sphere-approximation scheme. Energy-volume and magnetovolume studies of bulk Gd, Mo, and W are presented. Use of the LSDA in the study of Gd indicates that the antiferromagnetic structure is energetically favorable at the equilibrium lattice parameter which is 3% smaller than the experimental value. Application of the PBE functional predicts the experimentally observed ferromagnetic ground state at an equilibrium lattice parameter close to (+0.5%) the experimental value. Magnetovolume studies of Mo and W predict that, although both these metals possess a nonmagnetic bcc ground state, they will exhibit antiferromagnetic behavior at large volumes regardless of whether the structure of the idealized unit cell is bcc, fcc, or hcp. Magnetic behavior as a consequence of volume expansion is also predicted to occur on the Mo or W sites within Gd/$X (X=\mathrm{M}\mathrm{o},\mathrm{W})$ bilayers. Moreover, for the case of a 5Gd/3Mo multilayer, constructed using the volume parameters of bulk Gd, the magnetic behavior of the Gd and Mo layers is nearly identical to that of the constituent bulk elements at the same volume. We have thus demonstrated that any possible occurrence of a magnetic moment on a Mo or W site within such a multilayer is a direct consequence of volume effects only.