Photoemission and x-ray absorption studies of valence states in (Ni,Zn,Fe,Ti)_3O_4 thin films exhibiting photoinduced magnetization

摘要

By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)_3O_4 thin films, which exhibits a cluster glass behavior with a spin-freezing temperature T)f of ～230 K and photoinduced magnetization (PIM) below T_f The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe~(3+)) and tetravalent (Ti~(4+)), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe~(2+) ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.