Growth and Properties of Epitaxial Thin films and Heterostructures of Multiferroic Bi_1-XBa_XFeO₃

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Epitaxial thin films of Bi_1-xBa_xFeO₃ have been deposited by sputtering on LaAlO₃ and SrTiO₃ substrates with and without conducting buffer layers of paramagnetic LaNiO₃ and ferromagnetic La_0.7Sr_0.3MnO₃, and their structural, magnetic and ferroelectric properties have been investigated. It has been shown from magnetic and ferroelectric characterization that Bi_1-xBa_xFeO₃ epitaxial films in a thickness of 300 nm exhibited reasonable multiferroic properties at room temperature. Spin-filter junctions consisting of a La_0.7Sr_0.3MnO₃/ Bi_1-xBa_xFeO₃/LaNiO₃ epitaxial heterostructure have been fabricated using photolithography and ion milling. The junctions with a Bi_1-xBaxFeO₃ layer thickness of 4 nm exhibited nonlinear current-voltage (I-V) characteristics with the barrier height of 0.37 eV, and MR effect at 4.2 K, indicating that the Bi_1-xBa_xFeO₃ ultrathin layers serves as ferromagnetic tunnel barriers in spin-filter junctions.