Ferromagnetism Driven by Intrinsic Point Defects in HfO₂

In view of recent experimental reports of unexpected ferromagnetism in HfO₂ thin films, we carried out first-principles investigations looking for magnetic order possibly brought about by the presence of small concentrations of intrinsic point defects. Ab initio electronic structure calculations using density functional theory show that isolated cation vacancy sites in HfO₂ lead to the formation of high-spin defect states. Furthermore these appear to be ferromagnetically coupled with a rather short range magnetic interaction, resulting in a ferromagnetic ground state for the whole system. More interestingly, the occurrence of these high-spin states and ferromagnetism is in the low symmetry monoclinic phase of HfO₂. This is radically different from other systems previously known to exhibit point defect ferromagnetism, warranting a closer look at the phenomenon.