Ferromagnetism induced by magnetic vacancies as a size effect in thin films of nonmagnetic oxides

Abstract

A theory of magnetization induction in thin films of binary nonmagnetic oxides has been developed. We show that the origin and the main peculiarities of magnetization experimentally observed in thin films of such nonmagnetic oxides as SnO2, CeO2, Al2O3, ZnO, MgO, and HfO2 can be explained if oxygen vacancies are considered as magnetization sources. Our calculations have shown that the oxygen vacancies become magnetic at the film–substrate interface, and a long-range ferromagnetic order appears in thin films at room and higher temperatures. The role of substrate turns out to be extremely important for the accumulation of magnetic vacancies taking place owing to the film-substrate misfit stress. The vacancy accumulation has been shown to result in the film magnetization increase, which agrees with experimental data.