高圧合成法を用いた強磁性強誘電体ビスマスダブルペロブスカイトの探索

概要

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Multiferroic materials where ferromagnetism and ferroelectricity coexist are rare. We have succeeded in synthesizing new multiferroic materials Bi2M MnO6 (M = Ni, Co) at high pressure of 6 GPa. The crystal structures of these compounds are a heavily distorted double-perovskite (space group C2), with M 2+ and Mn4+ ions ordered in a rock-salt configuration. The monoclinic unit cell of Bi2NiMnO6 is a = 9.4630(1), b = 5.42553(8), c = 9.5352(1) Å, and β= 107.840(1)°, and that of Bi2CoMnO6 is a = 9.4886(2), b = 5.4444(1), c = 9.5678(2) Å, and β= 107.603(1)°. A polarized 6s2 lone pair in Bi3+ causes the noncentrosymmetric structural distortion, which leads to ferroelectric property. On the other hand, NaCl-type ordering of M 2+ with eg electrons and Mn4+ without eg electron produces ferromagnetic exchange paths, -M 2+-O2--Mn4+-, according to the Kanamori-Goodenough rules. The ferroelectric and the ferromagnetic transition temperatures of Bi2NiMnO6 are 455 and 140 K, respectively. The ferroelectric transition temperature of Bi2CoMnO6 is above 600 K, while the ferromagnetic transition temperature is 95 K.
社団法人粉体粉末冶金協会の論文
2005-12-15