Preparation and magnetic properties of DC-sputtered porous HfO2 films

Ordered hafnium oxide films were successfully prepared on porous anodic alumina substrates using DC reactive magnetron sputtering, and remarkable room-temperature ferromagnetism has been observed in them. A saturation magnetization (M-s) value as high as 128 emu/cm(3) was obtained for 80 nm thick HfO2 film with the external field perpendicular to the film surface. Experimental and theoretical results indicate that the single charged oxygen vacancies and the unique porous structure of the films are responsible for the large ferromagnetism. The coupling between single charged oxygen vacancies may be explained either by direct exchange interactions between oxygen vacancies (Vo(+)-Vo(+)) or by mediation of conduction electrons (Vo(+)-e(-)-Vo(+)). These observations may be useful in the development of HfO2-based spintronics devices. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.