Multiferroic Bi 2 NiMnO 6 with a Double-Perovskite Structure: High-Pressure Synthesized Bulk and Epitaxially Grown Thin
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1034-K04-07
Multiferroic Bi2NiMnO6 with a Double-Perovskite Structure: High-Pressure Synthesized Bulk and Epitaxially Grown Thin Films Yuichi Shimakawa Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan ABSTRACT A new multiferroic compound Bi2NiMnO6 was synthesized in both bulk and thin-film forms. Bulk samples were prepared under a high pressure condition at 6 GPa, and thin-film samples were epitaxially grown on single-crystal SrTiO3 substrates by a pulsed-laser deposition method. The crystal structure of the material is a double perovskite, in which Ni2+ and Mn4+ ions are ordered in a rock-salt configuration. Bi3+ ions at the A-site cause a noncentrosymmetric (C2) structural distortion which allows a spontaneous ferroelectric polarization at room temperature. Ni2+–O–Mn4+ magnetic paths lead to ferromagnetism through the superexchange interaction according to the Kanamori-Goodenough rule. A coupling between the ferromagnetic and ferroelectric interactions appears to exist, but it is quite small. INTRODUCTION Multiferroic materials, in which ferromagnetic and ferroelectric orders coexist, have attracted a lot of attention both in fundamental physics and technological applications. Recent much interest on multiferroic oxides is being given to a BiFeO3 perovskite. Bulk BiFeO3 intrinsically shows multiferroic properties; i.e., ferroelectric polarization and weak magnetism at room temperature. The rhombohedrally distorted perovskite structure leads to spontaneous polarization below the transition temperature (TC = 1103 K). The magnetic property originates from a residual moment of a spin canting of the antiferromagnetically ordered spin structure (TN = 643 K) [1]. On the other hand, epitaxially-grown constrained BiFeO3 thin films showed enhanced multiferroic properties. Large spontaneous polarization and enhanced magnetization were observed at room temperature in the constrained thin-film samples [2, 3], though the properties of the BiFeO3 films are still under debate. Recent discoveries of strong interplay between magnetism and ferroelectricity in TbMnO3 [4] and TbMn2O5 [5] have also stimulated a lot of interest in strong coupling between ferroelectric and ferromagnetic order parameters. In these compounds (non-)collinear spiral magnetic structures induce ferroelectric spontaneous polarization [6] and the significant changes in dielectric properties under applied magnetic fields are observed. Recent intensive studies on new materials and new phenomena also accelerate research for potential applications of multiferroic materials, such as new kinds of nonvolatile storage devices. We report, in this paper, a new multiferroic Bi2NiMnO6 compound with a doubleperovskite structure. We have succeeded in stabilizing this compound by means of high-pressure synthesis [7] and epitaxial growth of the thin film [8, 9]. Bi3+ ions at the A site in the perovskite structure cause ferroelectric structural distortion. In contrast to the antiferromagnetic spin ordering in BiFeO3, Bi2NiMnO6 shows ferromagnetic s
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