Magnetism in hafnium dioxide

TLDR

Thin‑film HfO₂ grown by pulsed‑laser deposition on sapphire, YSZ, or silicon displays ferromagnetic behavior with Curie temperatures above 400 K, and lattice defects are believed to be the source of this magnetism. The magnetic moment is independent of film thickness but ranges from 150 to 400 μB nm⁻² per substrate area, shows pronounced anisotropy tied to texture and substrate orientation, and pure powder develops a weak moment upon vacuum heating that is removed by oxygen annealing.

Abstract

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.