Oxygen vacancy mediated room temperature ferromagnetism in Cu-doped LiNbO3 thin films

Abstract

Room temperature ferromagnetic Cu-doped LiNbO3 thin films with Cu contents of 2–8 at.% were deposited by RF-magnetron sputtering. X-ray absorption spectroscopy together with multiple-scattering ab initio theoretical calculations at Cu K-edge revealed the incorporation of Cu ions into Nb sites in the LiNbO3 host lattice with divalent valence state. The detailed local structural analysis also confirmed that oxygen vacancies are present in the nearest coordination shell of the Cu atoms. The activated ferromagnetism in the Cu-doped LiNbO3 is intrinsic and probably originates from indirect interactions between the oxygen vacancies and dopant ions, which forms bound magnetic polarons and overlapping polaron orbitals, resulting in stable ferromagnetic ordering. These results present a practical method of triggering room temperature ferromagnetism in non-magnetic Cu element doped LiNbO3 systems with oxygen defects, which helps elucidate the origin of ferromagnetism in perovskite ferroelectric oxides.