Spin-ladder iron oxide:: Sr3Fe2O5
Spin-ladder iron oxide:: Sr3Fe2O5
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DOI：
10.1002/anie.200801146
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Andre, Gilles
中科院分区：
文献类型：
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作者：
Kageyama, Hiroshi;Watanabe, Takashi;Andre, Gilles
自旋梯在概念上是反铁磁(AF)二维(2D)正方形晶格的单向截面，如图1所示，在过去的二十年里引起了相当大的关注。理论预言，当支数n为偶数时，S=1/2阶梯的基态是有隙单重态液态场，而当n为奇数时，基态为无间隙单重态液态场。此外，当偶数支梯中掺杂适量载流子时，短程AF自旋关联将导致超导。实验的对应物是观察到了SrCu2O3(n=2)和Sr2Cu3O5(n=3)的有隙基态和无间隙基态，[2]以及在高压下(Sr，Ca)14Cu24O41+x(n=2)中出现了超导电性。[4]理论研究的动机一直是测试一维(1D)S=1/2 AF链系统(n=1)如何与2D正方形晶格(n=1)相关联，这带来了各种理论困难，而且还远未被理解。在实验上，SRN±1CuO2n±1是唯一一个广义的自旋梯形系统的例子[5]，尽管两条腿的梯子的组成和结构已经扩展到CaV2O5，Cu2(C5H12N2)Cl4，(C5H12N)2CuBr4，[Ph(NH3)-([18]冠-6)][Ni(Dmit)2](dmit=二硫杂环戊烯)和[(Dtttf)2][Au(Mnt)2](dt-ttf=二硫富瓦烯，mnt=顺丁烯二硫杂环戊烯)[6]从理论和实验的观点来看，将这些梯形系统扩展到n和S是非常可取的并且还涉及可能的偏斜，例如铁磁和AF相互作用的混合。扭曲的一个例子是大间隙(>；[7]D9铜(II)氧化物最显著的结构特征是易于形成方形平面的CuO4单元，由于Jahn-Teller效应而稳定。[8]这种2D配位几何构型在沿支腿和梯级的梯形内提供了很强的铜-氧-铜超交换作用，而垂直于正方形平面(Kz)的铜··铜相互作用可以忽略不计，因为铜(II)离子具有磁性惰性，与铜酸盐不同，氧化铁的配位几何构型几乎只限于三维多面体，如八面体和四面体。然而，最近由Hayward和Rosseinsky及其同事发起和开发的低温氢化钙作为还原剂[9]克服了这一限制。[10，11]立方钙钛矿型SrFeIVO_3与CaH_2的低温反应导致稳定的SrFeIIO_2在高自旋Fe~(2+)离子周围形成方形平面氧配位环境。[12]本文报道了由双层钙钛矿结构的Sr3FeIV2O7与CaH2反应合成的新型自旋梯形铁氧化物Sr3FeI2O5。与SrFeO2的合成一起，这为具有方形平面配位的铁(II)氧化物的固态化学开辟了新的途径，其中可能包括系列梯形系统SRN+1FeO2n+1，以及多销梯形的固态物理。
Spin ladders, which conceptually are unidirectional sections of an antiferromagnetic (AF) two-dimensional (2D) square lattice, as schematically illustrated in Figure 1, have attracted considerable attention in the last two decades. Theories predict that the ground state of an S= 1/2 ladder is a gapped singlet spin liquid state when the leg number n is even, but is a gapless singlet spin liquid state when n is odd.[1] Moreover, short-range AF spin correlation should lead to superconductivity when modest carriers are doped in even-legged ladders. Experimental counterparts are the observation of the gapped and gapless ground states of SrCu2O3 (n= 2) and Sr2Cu3O5 (n= 3), respectively,[2] and the appearance of superconductivity in (Sr, Ca) 14Cu24O41+ x (n= 2) under high pressure.[3] Another S= 1/2 two-legged Cu2+ ladder, namely, La1ÀxSrxCuO2. 5, shows anomalous behavior associated with its nearly critical ground state.[4] The motivation of theoretical investigations has been to test how the one-dimensional (1D) S= 1/2 AF chain system (n= 1), which is rigorously solved even when doped with carriers, can be related to the 2D square lattice (n= 1), which presents various theoretical difficulties and is far from being understood. Experimentally, SrnÀ1CunO2nÀ1 is the only example of a generalized spin-ladder system,[5] though the composition and structure of a two-legged ladder has been extended to CaV2O5, Cu2 (C5H12N2) Cl4,(C5H12N) 2CuBr4,[Ph (NH3)-([18] crown-6)][Ni (dmit) 2](dmit= dithiolene) and [(DTTTF) 2][Au (mnt) 2](DT-TTF= dithiophene tetrathiafulvalene, mnt= maleonitrile dithiolate).[6] It is highly desirable from both theoretical and experimental viewpoints to extend these ladder systems with respect to n and S, and also with respect to possible skews such as mixing of ferromagnetic and AF interactions. An example of skew is the dramatic switching of the large-gapped (> 400K) singlet spin liquid of SrCu2O3 to an AF ordered state by the nonmagnetic substituent Zn2+, even at Zn/Cu 1%.[7] The most pronounced structural characteristic of d9 copper (II) oxides is the favored formation of squareplanar CuO4 units, which are stabilized due to the Jahn–Teller effect.[8] This 2D coordination geometry provides strong Cu-O-Cu superexchange interactions within a ladder along the legs and rungs, while Cu··· Cu interactions normal to the square plane (kz) are negligibly small because the copper (II) ions have a magnetically inert, filled (dz2↑↓) configuration along this direction and also because an intervening oxygen atom is lacking.Unlike the case of cuprates, the coordination geometries in iron oxides have been almost exclusively restricted to 3D polyhedra such as octahedra and tetrahedra. However, this restriction was recently overcome [9] by using calcium hydride at low temperatures as a reductant, as initiated and developed by Hayward, Rosseinsky and co-workers.[10, 11] Low-temperature reaction of cubic perovskite SrFeIVO3 with CaH2 led to stable SrFeIIO2 with a square-planar oxygen coordination environment around the high-spin Fe2+ ion. The structure is isostructural with the “infinite”-layer cupric oxides.[12] Herein we report the synthesis of novel spin-ladder iron oxide Sr3FeII 2O5 through reaction of double-layered perovskite Sr3FeIV 2O7 with CaH2. Together with the synthesis of SrFeO2, this opens up new avenues for the solid-state chemistry of iron (II) oxides with square-planar coordination, which potentially includes the serial ladder system Srn+ 1FenO2n+ 1, and for the solid-state physics of multiplespin ladders.