Photoemission and x-ray absorption studies of valence states in (Ni,Zn,Fe,Ti)$_{3}$O$_{4}$ thin films exhibiting photo-induced magnetization

TL;DR

This study uses photoemission and x-ray absorption spectroscopy to analyze the electronic structure of (Ni,Zn,Fe,Ti)$_{3}$O$_{4}$ thin films, revealing valence states and a charge-transfer mechanism underlying photo-induced magnetization.

Contribution

It provides new insights into the valence states and charge-transfer mechanisms in (Ni,Zn,Fe,Ti)$_{3}$O$_{4}$ thin films exhibiting photo-induced magnetization.

Findings

Ni and Zn ions are divalent.

Fe ions are mostly trivalent, Ti ions are tetravalent.

Ti doping increases Fe$^{2+}$ ions, supporting charge-transfer mechanism.

Abstract

By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)$_{3}$O$_{4}$ thin films, which exhibits a cluster glass behavior with a spin-freezing temperature $T_f$ of $\sim 230$ K and photo-induced 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.