First-principles calculations for the structural and magnetic properties of ordered NiFe(001) thin films with and without a Ta overlayer

The first-principles calculations within the local density approximation using the full potential linearized augmented plane wave (FLAPW) method were performed to investigate the structural and magnetic properties of the Ta/NiFe interface for both clean Ni_xFe_1-x (001) thin films and with a Ta overlayer. To study the composition dependence, we adopted x=0.5 (L1₀ structure with either Fe or Ni layers on the surface) and 0.75 (L1₂ structure with mixed Fe-Ni layers or with Ni on the surface). The equilibrium overlayer/substrate distance and the preferred site position of Ta were obtained by structural optimization employing atomic-force calculations and total energy comparisons for several possible adsorption sites of Ta. By comparing with results for the clean surface of five-layer Ni_xFe_1-x (001) films, we found that Ta has a significant detrimental effect on the magnetic properties of NiFe with its induced magnetic moment coupled ferro- or antiferro-magnetically with the substrate depending sensitively on the surface layer.