Abstract
The effect of an ultrathin TiO2 capping layer on an anatase Ti0.95Co0.05O2−δ (001) epitaxial thin film on magnetism at 300 K was investigated. Films with a capping layer showed increased magnetization mainly caused by enhanced out-of-plane magnetization. In addition, the ultrathin capping layer was useful in prolonging the magnetization lifetime by more than two years. The thickness dependence of the magnetic domain structure at room temperature indicated the preservation of magnetic domain structure even for a 13 nm thick film covered with a capping layer. Taking into account nearly unchanged electric conductivity irrespective of the capping layer’s thickness, the main role of the capping layer is to prevent surface oxidation, which reduces electron carriers on the surface.
Highlights
A ferromagnetic oxide semiconductor (Ti,Co)O2 attracts much attention due to its high Curie temperature, promising for room temperature semiconductor spintronics [1,2,3,4]
The carrier-mediated exchange interaction plays an important role evidenced by its ferromagnetism controlled via electric-field gating [5], chemical doping [6], and the Curie temperature changed by carrier density [7]
Reflection high energy electrondiffraction diffraction (RHEED) patterns of the buffer layer, the (Ti,Co)O2 film, and the capping layer showed a streak pattern with the flat sample surface observed via AFM (Figure 1), indicating the epitaxial growth and pattern with the flat sample surface observed via AFM (Figure 1), indicating the epitaxial growth and sharpsharp interface between each layer
Summary
A ferromagnetic oxide semiconductor (Ti,Co)O2 attracts much attention due to its high Curie temperature, promising for room temperature semiconductor spintronics [1,2,3,4]. A magnetically dead layer at the surface observed via X-ray magnetic circular dichroism showed significantly reduced magnetization on the surface [9], which is an obstacle for the implementation of various thin film devices. In the case of (Ti,Co)O2 , the magnetically dead layer was at least ~5 nm thick [9] and could be attributed to a surface oxidation and/or a depletion layer due to the different surfaces and bulk electronic structures observed via soft and hard X-ray photoemission spectroscopy [12].
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