Discovery of Ferromagnetic-Half-Metal-to-Insulator Transition in K_2Cr_8O_(16)

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作   者：

Kunihiro Hasegawa;  Masahiko Isobe;  Touru Yamauchi;  Hiroaki Ueda;  Jun-Ichi Yamaura;  Hirotada Gotou;  Takehiko Yagi;  Hirohiko Sato;  Yutaka Ueda; 

作者机构：

Institute for Solid State Phvsics;  Materials Design and Characterization Laboratory;  Japan;  Institute for Solid State Physics;  University of Tokyo;  Kashiwa 277-8581;  Department of Physics;  Chuo University;  Tokyo 112-8551;  Division of New Materials Science; 

关键词：

metal-insulator transitions and other electronic transitions;  other ferromagnetic metals and alloys; 

期刊名称：

Physical review letters

i s s n：

0031-9007

年卷期：

2009 年 103 卷 14 期

页   码：

146403.1-

页   码：

摘   要：

The hollandite chromium oxide K_2Cr_8O_(16) has been synthesized in both powder and single-crystal form under high pressure. Combining electrical resistivity, magnetic susceptibility, and x-ray diffraction, we found that K_2Cr_8O_(16) is a ferromagnetic metal (or half-metal) with T_C = 180 K and shows a transition to an insulator at 95 K without any apparent structural change but retaining ferromagnetism. K_2Cr_8O_(16) is quite unique in three aspects: It has a rare mixed valence of Cr~(3+) and Cr~(4+); it has a metal (or half-metal)-to-insulator transition in a ferromagnetic state; and the resulting low-temperature phase is a rare case of a ferromagnetic insulator. This discovery could open a new frontier on the relation of magnetism and conducting properties in strongly correlated electron systems.