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Promoting Exchange Bias Coupling in Fe/MgO(001) Films by Controlling Interface Oxide Distribution
B.-Y. Wang*, C.-J. Chen, K. Lin, C.-Y. Hsu, J.-Y. Ning, M.-S. Tsai, T.-H. Chuang, D.-H. Wei, and S.-C. Weng
MgO-based magnetic heterostructures are crucial building blocks in state-of-the-art spintronic devices. In this study, we performed thermal annealing to control the formation and distribution of FeO across the interface of a Fe-MgO system. The exchange bias phenomenon (i.e., a horizontal shift of magnetic hysteresis loops) was extended from involving only interface spins to involving the full-volume magnetization of the Fe film. The extended and reinforced exchange bias coupling in the annealed Fe/MgO(0 0 1) films can be attributed to the formation of a Fe-FeO matrix-like structure at the Fe/MgO interface under an increasing degree of interface roughness and the reduction or diffusion of oxygen from the interfacial oxides, as indicated by X-ray absorption near edge structures and X-ray reflectivity measurements. Moreover, the thermal stability of exchange bias coupling in the annealed Fe/MgO(0 0 1) films (maximum value at approximately 600 K) was considerably higher than that in conventional thin-film-based Fe/FeO structures (approximately 50 K).