Magnetoresistance in double-layered perovskite-type manganese oxides

尝试了双钙钛矿结构NdBaMn_2O_6的单晶生长，该结构位于铁磁金属、反铁磁电荷有序绝缘体和反铁磁二维金属之间的多临界点附近。运输测量的孪生单晶显示显着降低尼尔温度约280 K的应用程序的磁场。在c轴方向观察到沿着的巨负磁电阻，在240 K时电阻率降低了1/30.用X射线漫散射研究了A位有序RBaMn 2 O 6体系中上述3个相之间的竞争.拉曼散射光谱也观察到该体系中的电荷/轨道有序效应，其中电荷/轨道有序的MnO 2片沿着c轴的攻击方式与传统的A位无序的钙钛矿锰氧化物（R，A）MnO 3不同。中子衍射的详细研究表明，NdBaMn 2 O 6中的铁磁有序的MnO 2片沿着c轴反铁磁堆叠。晶格参数a和B在低于Neel温度时突然伸长，而c长度收缩。晶格参数的这种异常清楚地表明，x2-y2轨道的铁型有序同时形成在Mn自旋扇区的有序。

Single-crystal growth of double-perovskite NdBaMn2O6, which locates near the multicritical point among ferromagnetic metal, antiferromagnetic charge-ordered insulator, and antiferromagnetic two-dimensional metal, was tried. Transport measurements of twin single crystals show the significant reduction of Neel temperature of about 280 K by application of a magnetic field. Giant negative magnetoresistance along the c axis was observed ; resistivity at 240 K decreases by 1/30.Competing among the abovementioned three phases in the A-site ordered RBaMn2O6 system was investigated by X-ray diffuse scattering. Raman scattering spectroscopy was also performed to observe the effect of charge/orbital ordering in this system, where charge/orbital ordered MnO2 sheets attack along the c axis in a different manner from the conventional A-site-disordered perovskite manganese oxides (R,A)MnO3.Detail study of neutron diffraction in NdBaMn2O6 shows that ferromagnetically ordered MnO2 sheets antiferromagnetically stack along the c-axis. Lattice parameters a and b are suddenly elongated below Neel temperature, while the c length shrinks. This anomaly in lattice parameters clearly demonstrates that the ferro-type ordering of x2-y2 orbitals is formed simultaneously at the ordering of the Mn spin sector.