Magnetic and electrical properties ofLBaMn2O6−γ(L=Pr,Nd, Sm, Eu, Gd, Tb) manganites
Magnetic and electrical properties ofLBaMn2O6−γ(L=Pr,Nd, Sm, Eu, Gd, Tb) manganites
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LBaMn2O6−γ(L=Pr,Nd,Sm,Eu,Gd,Tb)锰酸盐的磁电性能
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
K. Bärner
中科院分区：
文献类型：
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作者：
S. Trukhanov;I. Troyanchuk;M. Hervieu;H. Szymczak;K. Bärner
研究了阳离子有序无序现象对LBaMn2O6-γ(L=Pr，Nd，Sm，Eu，Gd，Tb)系列新型CMR钙钛矿结构、磁性和电输运性质的影响。对于每个稀土离子，用拓扑定向还原-氧化法合成了三个化合物。结构研究表明，在空气中得到的氧化学计量比化合物LBaMn2O6是立方的，含有无序的L 3+和Ba2+阳离子，而缺氧的LBaMn2O5是四方的，含有有序的L 3+和Ba2+，并沿c方向交替堆积稀土和含钡的层。这种晶体结构类似于YBaCuFeO5相关的晶体结构。另一种氧化学计量比的LBaMn2O6化合物也是四方的，保留了L 3+和Ba2+离子的有序性。值得注意的是，重新氧化的EuBaMn2O6化合物具有正交晶胞。观察到，这种类型的阳离子有序化导致向顺磁态的转变温度显著提高。例如，无序的EuBaMn2O6化合物具有类似于自旋玻璃的磁性，其磁矩的冻结温度Tf为40K，而有序的EuBaMn2O6化合物是居里点为TC 260K的非均匀铁磁体，其电阻率行为与磁化强度有关。在T_c以下，Pr、Nd、Sm基化合物经历了向金属态的转变，并表现出磁电阻峰。认为复氧化合物的磁性和电学性质的显著变化是L/巴有序化的结果，并可用考虑钙钛矿亚晶格中离子尺寸效应的180°间接超交换作用的Goodality-Kanamori规则来解释。
Influence of cation order-disorder phenomena on the crystal structure, magnetic, and electrical transport properties of new CMR perovskites for LBaMn 2 O 6 - γ (L=Pr, Nd, Sm, Eu, Gd, Tb) series has been investigated. For each rare-earth ion three compounds have been synthesized by the topotactic reduction-oxidation method. Structural investigations have shown the oxygen-stoichiometry LBaMn 2 O 6 compound obtained in air to be cubic with disordered L 3 + and Ba 2 + cations whereas the oxygen-deficient LBaMn 2 O 5 is tetragonal with ordered L 3 + and Ba 2 + and alternate stacking of rare earth and barium containing layers along c. This crystal structure is similar to the YBaCuFeO 5 related one. Another form of oxygen-stoichiometry LBaMn 2 O 6 compound obtained by reoxidation of oxygen-deficient LBaMn 2 O 5 is also tetragonal and retains the ordering of L 3 + and Ba 2 + cations. It is notable that the reoxidized EuBaMn 2 O 6 compound has an orthorhombic unit cell. It is observed that this type of cation ordering leads to considerable increase of transition temperature to paramagnetic state. For example, disordered EuBaMn 2 O 6 compound has magnetic properties similar to spin glass and shows freezing temperature of magnetic moments T f 40 K while ordered EuBaMn 2 O 6 is an inhomogeneous ferromagnet with Curie point T C 260 K. Electrical resistivity behavior correlates with magnetization. Below the T C the Pr, Nd, Sm based compounds undergo a transition to metallic state and demonstrate a peak of magnetoresistance. It is supposed that the remarkable changing of the magnetic and electrical properties of the reoxidized compounds is a consequence of the L/Ba ordering and can be explained on the base of the Goodenough-Kanamori rules for 180° indirect superexchange interactions taking into account an ion size effect in A sublattice of perovskite.