The unoccupied part of the electronic structure of the O-deficient hafnium oxide (HfO~1.8) was investigated using soft X-ray absorption spectroscopy at 0K and Hf N3 edges. Band-tail states beneath the unoccupied Hf 5d band were observed in the O K-edge spectra. Combined with ultraviolet photoemission spectrum, this indicated the non-negligible occupation of the Hf 5d state. However, Hf N3-edge magnetic circular dichroism spectrum revealed the absence of a long-range ferromagnetic spin order in the oxide. Thus, the small amount of d electron gained by the vacancy formation did not exhibit intersite correlation.

Influence of Oxygen Vacancies on the Electronic Structure of HfO2 Films. D.Y.Cho, J.M.Lee, S.J.Oh, H.Jang, J.Y.Kim, J.H.Park, A.Tanaka: Physical Review B, 2007, 76[16], 165411, (5pp)