Magnetism of two-dimensional defects in Pd: Stacking faults, twin boundaries, and surfaces

Abstract

Careful first-principles density functional calculations reveal the importance of hexagonal versus cubic stacking of close-packed planes of Pd as far as local magnetic properties are concerned. We find that, contrary to the stable face-centered-cubic phase, which is paramagnetic, the hexagonal-close-packed phase of Pd is ferromagnetic with a magnetic moment of $0.35\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}∕\mathrm{atom}$. Our results show that two-dimensional defects with local hcp stacking, like twin boundaries and stacking faults, in the otherwise fcc Pd structure, increase the magnetic susceptibility. The (111) surface also increases the magnetic susceptibility and it becomes ferromagnetic in combination with an individual stacking fault or twin boundary close to it. On the contrary, we find that the (100) surface decreases the tendency to ferromagnetism. The results are consistent with the magnetic moment recently observed in small Pd nanoparticles, with a large surface area and a high concentration of two-dimensional stacking defects.