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 $400\mathrm{K}$. The moment does not scale with film thickness, but in terms of substrate area it is typically in the range $150–400{\mu }_{\mathrm{B}}{\mathrm{nm}}^{-2}$. 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.