Spin transition in a four-coordinate iron oxide

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四本の手をもつ金属原子の磁性の変換に成功－磁気記録、スイッチ素子の革新につながるか－. 京都大学プレスリリース. 2009-07-21. http://www.kyoto-u.ac.jp/ja/news_data/h/h1/news6/2009/090721_1.htmSpin 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 3d4 to 3d7 metals, such as Fe(II). A five-coordinate centre is only rarely seen. Here we report that under pressure SrFe(II)O2, 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 (dxz,dyz) states are filled. These results highlight the square-planar coordinated iron oxides as a new class of magnetic and electric materials.