Chemical-substitution dependence of magnetization strength in room- temperature ferromagnetism of dilute magnetic oxides: Valence and spin state of slightly doped cobalt in (In,Al)2O3

Abstract

This study investigates the valence and spin states of cobalt ions and the magnitude of room-temperature ferromagnetic magnetization in In1.9−xAlxCo0.1O3 (0≤x≤0.3) prepared by a chemical solution method. According to X-ray photoelectron spectroscopy, the Co ions in the Al-free sample (x=0) existed in a mixed state of trivalent Co3+ and divalent Co2+. The abundance ratio of Co2+ increased with Al content, and only divalent ions were present at x=0.3. A magnetic susceptibility analysis showed that both the spin and orbital degrees of freedom were magnetized in Co2+, whereas Co3+ was in a low-spin state. Co3+ was converted to Co2+ by vacuum annealing. The higher the conversion ratio of Co3+ to Co2+, the stronger was the room-temperature ferromagnetism.