Magnetism and deformation of epitaxial Pd and Rh thin films

Abstract

By means of ab initio calculations, we investigated structural and magnetic properties of Pd and Rh thin films, determining their lattice parameters and epitaxial stresses when they are grown on various substrates, and provided a comparison with available experimental data. Further, we studied in detail the magnetic properties of Pd in the higher-energy hcp structure and of Rh in the higher-energy bcc structure. The results predict that the hcp(112¯0) Pd films [grown by epitaxy on the Nb(001) substrate] should not be ferromagnetically ordered. Concerning the hcp Pd, we mainly investigated the influence of the hcp c/a ratio on the hcp film stability and on the ferromagnetic order. It turns out that the c/a ratio has to be below 1.622 to induce the ferromagnetic order in hcp Pd. We proposed a technological route for obtaining ferromagnetic hcp(112¯0) Pd films and explained the experimentally observed ferromagnetism in twinned Pd nanoparticles induced by strain. We also found that bcc Rh is ferromagnetically ordered, but it cannot be stabilized in the form of thin films. Therefore, we investigated the dependence of ferromagnetic order in bct Rh on the tetragonal c/a ratio and compared our results with experiments performed on Rh/Fe(001) multilayers.