Colossal Magnetoresistance in Cuprates?

近年来，由于观察到了层状铜酸盐材料的高温超导电性，人们对其进行了大量的研究。与普通导体不同，超导体在临界温度T_c以下表现出零电阻，技术应用包括用于核磁共振扫描仪的超导磁体、欧洲核子研究中心等高能加速器中的波束导向磁体和磁悬浮列车。目前，在铜酸盐材料HgBa2Ca2Cu3O8+y中观察到的超导电性的记录温度为-113℃。另一个已被大量研究的现象是在钙钛矿锰氧化物和Sr2FeMoO6中观察到的负磁电阻现象。一种负磁阻性材料在施加磁场时表现出电阻率的减小，并且这种化合物的电流应用包括存储器存储设备。我们最近在Ruthenocuprate材料RuSr2Nd2-x-yCexYyCu2O10中发现了大的负磁电阻，范围在x=0.7-0.95之间；-在7特斯拉的磁场中，在4K下观察到高达49%的MR，这与自旋极化的导体，如CMR锰氧化物钙钛矿和Sr2FeMoO6(在更高的温度)相当。在x=0.6(T_c~40K)时，该材料还观察到了超导电性。这是第一次在铜氧化物材料中观察到大的体负磁阻，这种材料在较高的铜氧化态下也表现出超导电性。为了进一步研究这一现象，我们建议合成和研究新的磁铜酸盐，如1222MSr2R0.9Y0.2Ce0.9Cu2O10-d和1212MSr2RCu2O7+d(M=Co，Fe，Os，Mn，Cr，Mo，Ir，Cu；R=Nd，Pr)和铜尖晶石Cu1+xM2-xO4(M=Mn，Cr，Fe，Ni，x=0/0.2)，以确定在其他铜酸盐中观察到磁阻的可能性，并优化铜酸盐的磁阻性能。如果能够在较高温度下观察到大的负磁电阻，这项工作不仅具有重要的基础性意义，而且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