Origin of magnetically dead layers in spinel ferrites FeO grown on AlO; Effects of postdeposition annealing studied by XMCD

Nonaka, Yosuke*; Wakabayashi, Yuki*; Shibata, Goro ; Sakamoto, Shoya*; Ikeda, Keisuke*; Chi, Z.*; Wan, Y.*; Suzuki, Masahiro*; Tanaka, Arata*; Tanaka, Masaaki*; Fujimori, Atsushi*

We study the electronic and magnetic states of as-grown and annealed FeO(111)/AlO3(111) (Co, Ni) thin films with various thicknesses grown on Si(111) substrates with the -AlO(111)buffer layers by using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD), to investigate magnetically dead layers in these films. Although the magnetically dead layers in the as-grown samples are formed near the interface with the AlO buffer layer, we reveal that ferrimagnetic order is partially recovered by postdeposition annealing at 973 K for 48 hours in air. By analyzing the line shapes of the XAS and XMCD spectra, we conclude that, in the dead layers, there are a significant number of vacancies at the sites of the spinel structure, which may be the microscopic origin of the degraded ferrimagnetic order in the FeO thin films.