Colossal Magnetoresistance in Cuprates?

近年来，由于对层状铜酸盐材料的高温超导性的观察，人们对这种材料进行了大量的研究。与普通导体不同，超导体在临界温度Tc以下表现为零电阻，技术应用包括MRI扫描仪的超导磁体，CERN和磁悬浮列车等高能加速器中的光束转向磁体。目前，在铜材料HgBa2Ca2Cu3O8+y中观察到的超导性的记录温度为-113℃。另一个研究较多的现象是在钙钛矿锰矿和Sr2FeMoO6中观察到的负磁电阻。负磁阻材料在施加磁场时表现出电子电阻率的降低，这种化合物的当前应用包括存储设备。我们最近在钌酸盐材料RuSr2Nd2-x-yCexYyCu2O10中惊人地发现了大的负磁阻，在x = 0.7 - 0.95之间；在7特斯拉的电场中，在4 K下观察到高达49%的磁流变率，这与自旋极化导体如CMR锰氧化物钙钛矿和Sr2FeMoO6（在更高的温度下）相当。该材料在x = 0.6 （Tc ~ 40k）时也有超导现象。这是第一次在铜材料中观察到大体积负磁电阻，并且在较高的铜氧化态下也表现出超导性。进一步调查这一现象我们提出合成和研究的magnetotransport性质MSr2R0.9Y0.2Ce0.9Cu2O10-d 1222和1212等新magnetocuprates MSr2RCu2O7 + d (M =公司、铁、Os、锰、铬、钼、红外光谱、铜;R = Nd, Pr)和铜酸盐尖晶石Cu1 + xM2-xO4 (M =锰、铬、铁、镍、x = 0/0.2)为了确定观察的可能性:在其他铜酸盐和优化磁阻的铜酸盐的属性。这项工作不仅具有重要的基础意义，而且如果有可能在较高温度下观察到大的负磁阻，则可能具有实际应用价值

In recent years there has been much research into layered cuprates due to the observation of high temperature superconductivity in such materials. Unlike normal conductors a superconductor exhibits zero electrical resistance below a critical temperature Tc and technological applications include superconducting magnets for MRI scanners, beam steering magnets in high-energy accelerators such as CERN and magnetic levitation trains. At present the record temperature at which superconductivity is observed stands at -113 degrees C in the cuprate material HgBa2Ca2Cu3O8+y. Another phenomena that has been much studied is that of negative magnetoresistance observed in perovskite manganites and Sr2FeMoO6. A negative magnetoresistant material exhibits a reduction in electronic resistivity upon application of a magnetic field and current applications of such compounds include memory storage devices. We have recently made the surprising discovery of large negative magnetoresistance in the ruthenocuprate material RuSr2Nd2-x-yCexYyCu2O10 between x = 0.7 - 0.95; -MR of up to 49% have been observed at 4 K in a 7 tesla field which is comparable to spin-polarised conductors such as CMR manganese oxide perovskites and Sr2FeMoO6 (at higher temperatures). Superconductivity is also observed in this material for x = 0.6 (Tc ~ 40 K).This is the first time that large bulk negative magnetoresistance has been observed in a cuprate material which also exhibits superconductivity at higher copper oxidation states. To investigate this phenomenon further we propose to synthesise and study the magnetotransport properties of new magnetocuprates such as 1222 MSr2R0.9Y0.2Ce0.9Cu2O10-d and 1212 MSr2RCu2O7+d (M = Co, Fe, Os, Mn, Cr, Mo, Ir, Cu; R = Nd, Pr) and cuprate spinels Cu1+xM2-xO4 (M = Mn, Cr, Fe, Ni, x = 0 / 0.2) in order to determine the possibility of observing -MR in other cuprates and to optimise the magnetoresistive properties of the cuprates. This work will not only be of great fundamental importance but may also have practical applications if it is possible to observe large negative magnetoresistance at higher temperatures