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Ferromagnetic oxides such as perovskite manganite and spinel ferrite exhibit high magnetic transition temperature and attractive magnetoresistive properties, which make these materials excellent candidates for superior spin electronics devices. The electric field/light controls of magnetisms have been demonstrated in the manganite based heterostructures such as p-n junction and field effect transistor. In addition to 2-D type layered heterostructure, nano-channel (quasi 1-D type) structure is a new strategy to enhance interfacial properties. This structure will be used to prepare planar side-gate field effect devices which control carrier mediated physical properties in isolated nano-sized correlated oxides in a reversible way. Recent studies in manganites have suggested that the ground state of transition metal oxides tends to be inhomogeneous, consisting of ?electric phase separation?; which may bring anomalous responses against external perturbations in nano-scale. Here, the technique of Atomic Force Microscope (AFM) lithography was used to construct robust nano-structures of perovskite manganites down to 30 nm in size. The resulting (La,Ba)MnO3 nano-channel possessed no lithographic damage and exhibited bulk-like room temperature ferromagnetism down to 30 nm beyond electrical phase separation picture . On the contrary, the (La,Pr,Ca)MnO3 nano-channel with 500 nm width exhibited an extremely sharp drop in magnetoresistance against increase of the magnetic field at both 10 K and 50 K, while the 10 μm and the 1 μm channels showed moderate decrease . This result suggests that metallic transition of the single insulating domain, acting as a bottle neck in the channel, leads to digitalized magnetoresistance. As a new candidate for spin oxide hetero/nano-structures, we also report physical properties of ferroelectric gate-ferromagnetic FET structure using tunable ferromagnetic semiconductor of Fe3-x MxOx (M=Mn, Zn) [3, 4] and Fe3-x MnxOx nano-channel structure prepared by Mo nano-mask AFM lithography technique .
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Tanaka, H., Kawai, T., Yanagisawa, Y. et al. Construction of Ferromagnetic Oxides Nano-Channel Structures Toward Nano area-FET devices by AFM Lithography. MRS Online Proceedings Library 1000, 507 (2007). https://doi.org/10.1557/PROC-1000-L05-07