Institute of Quantum Science, Nihon University, Chiyoda, Tokyo 101-8308, Japan.
Nat Chem. 2009 Aug;1(5):371-6. doi: 10.1038/nchem.289. Epub 2009 Jul 20.
Spin transition has attracted the interest of researchers in various fields since the early 1930s, with thousands of examples now recognized, including those in minerals and biomolecules. However, so far the metal centres in which it has been found to occur are almost always octahedral six-coordinate 3d(4) to 3d(7) metals, such as Fe(II). A five-coordinate centre is only rarely seen. Here we report that under pressure SrFe(II)O(2), which features a four-fold square-planar coordination, exhibits a transition from high spin (S = 2) to intermediate spin (S = 1). This is accompanied by a transition from an antiferromagnetic insulating state to a ferromagnetic so-called half-metallic state: only half of the spin-down (d(xz),d(yz)) states are filled. These results highlight the square-planar coordinated iron oxides as a new class of magnetic and electric materials.
自 20 世纪 30 年代初以来，自旋转变吸引了各个领域研究人员的兴趣，目前已经识别出数千种实例，包括矿物质和生物分子中的实例。然而，迄今为止，人们发现它发生的金属中心几乎总是八面体六配位的 3d(4) 到 3d(7) 金属，如 Fe(II)。五配位中心则很少见。在这里，我们报告在压力下 SrFe(II)O(2)，其具有四重四方平面配位，表现出从高自旋 (S = 2) 到中间自旋 (S = 1) 的转变。这伴随着从反铁磁绝缘态到铁磁所谓的半金属态的转变：只有一半的自旋向下（d(xz)，d(yz))态被占据。这些结果突出了四方平面配位的氧化铁作为一类新的磁性和电性材料。
