Colossal Magnetoresistance in Cuprates?

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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