Materials Design and Characterization Laboratory, Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan.
Phys Rev Lett. 2009 Oct 2;103(14):146403. doi: 10.1103/PhysRevLett.103.146403. Epub 2009 Oct 1.
The hollandite chromium oxide K2Cr8O16 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 K2Cr8O16 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. K2Cr8O16 is quite unique in three aspects: It has a rare mixed valence of Cr3+ and Cr4+; 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.
在高压条件下，我们成功地合成了粉末状和单晶态的钙钛矿型氧化铬钾 K2Cr8O16。通过电阻、磁化率和 X 射线衍射的测量，我们发现 K2Cr8O16 是一种铁磁金属（或半金属），居里温度 T(C)=180 K，在 95 K 时发生金属（或半金属）-绝缘体相变，没有明显的结构变化，但保留了铁磁性。K2Cr8O16 在三个方面具有独特性：它具有罕见的 Cr3+ 和 Cr4+ 混合价态；它在铁磁态下发生金属（或半金属）-绝缘体相变；低温相是罕见的铁磁绝缘体。这一发现为强关联电子体系中磁学和输运性质的关系开辟了一个新的研究领域。
