Magnetism in hafnium dioxide

Thin films of ${\mathrm{HfO}}_{2}$ produced by pulsed-laser deposition on sapphire, yttria-stabilized zirconia, or silicon substrates show ferromagnetic magnetization curves with little hysteresis and extrapolated Curie temperatures far in excess of $400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The moment does not scale with film thickness, but in terms of substrate area it is typically in the range $150--400\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}\phantom{\rule{0.2em}{0ex}}{\mathrm{nm}}^{\ensuremath{-}2}$. The magnetization exhibits a remarkable anisotropy, which depends on texture and substrate orientation. Pure ${\mathrm{HfO}}_{2}$ powder develops a weak magnetic moment on heating in vacuum, which is eliminated on annealing in oxygen. Lattice defects are the likely source of the magnetism.