Magnetic properties of HfO₂thin films

Abstract

We report on the magnetic and transport studies of hafnium oxide thin films grown by pulsed-laser deposition on sapphire substrates under different oxygen pressures, ranging from 10−7 to 10−1 mbar. Some physical properties of these thin films appear to depend on the oxygen pressure during growth: the film grown at low oxygen pressure (P≈10−7 mbar) has a metallic aspect and is conducting, with a positive Hall signal, while those grown under higher oxygen pressures (7 × 10−5≤P≤0.4 mbar) are insulating. However, no intrinsic ferromagnetic signal could be attributed to the HfO2 films, irrespective of the oxygen pressure during the deposition.

Physical properties and band structure of reactive molecular beam epitaxy grown oxygen engineered HfO2±x

“…Clearly, the linear diamagnetic behavior known for diamagnetic and stoichiometric HfO 2 could be observed, with no traces of ferromagnetic features. This is in good agreement with results found in literature claiming the absence of d 0 -ferromagnetism for undoped transition metal oxides [36]. For this study numer-ous films have been deposited and regularly measured, all results fail to give any evidence of d 0 -ferromagnetism in undoped hafnia.…”

“…Film darkening in hafnia as a function of oxidation conditions during growth, to our knowledge, has only been observed before by Hadacek et al, where a slight grey appearance for films grown under UHV conditions with PLD has been reported. [36] In comparison, for oxygen deficient SrTiO 3−δ , a change in color as a function of oxygen deficiency has been reported, where a glistening oxidized gem transmutes into a dull blue, conductive crystal. [37] We will later discuss the color change in HfO 2−x as a consequence of the formation of mid-gap defect bands due to oxygen vacancies allowing absorption at energies above 2 eV (620 nm).…”

Controlled oxygen vacancy induced p-type conductivity in HfO2−x thin films

“…In order to estimate the stoichiometry of our thin films, we have used X-ray photoelectron spectroscopy (XPS). Because in air always a surface layer of fully oxidized HfO 2 forms, ion beam cleaning of the samples becomes necessary which is, however, associated with oxygen preferential sputtering leading to unrealistic and sputter time dependent values of oxygen deficiencies in the range of have hole-type charge carriers in agreement with a previous observation [9]. In strongly reduced samples, we have measured a charge carrier concentration of about 6 times 10 21 per cm 3 .…”

The transport properties of oxygen vacancy-related polaron-like bound state in HfOx

“…The calculation is performed by using the spin polarized density functional theory44. For cell optimization, the supercell parameters are optimized in their charge states using PBE version of GGA with norm-conserving pseduopotentials.…”