Oxygen deficiency and valency reconstruction in multiferroic V-doped HfO 2

The interplay of oxygen deficiency and vanadium multiple valency in the candidate multiferroic V-doped P c a 2 1 hafnia HfO 2 is studied by first-principles calculations. Low-lying V majority gap states accept electrons from oxygen-vacancy donors, reducing their formation energy, and converting nominal V 4 + centers into V 3 + . The resulting local magnetization and screening changes are reflected in the calculated V core-level shifts, which are consistent with the experimentally observed x-ray photoelectron spectroscopy signatures. The calculated V 3 + / V 4 + population ratio determined by oxygen vacancies only matches experiment in reducing conditions, suggesting that additional electron reservoirs may contribute under atomic-layer-deposition growth conditions. A similar scenario also seems to apply to the recently observed multiferroicity in Cr-doped hafnia, where oxygen deficiency is expected from the synthesis route.