Probing the spin-glass and magnetoresistance in FeSr_{2Y_{1.7Ce_{0.3Cu_{2O_{10-δ

We have measured the electronic transport and magnetic properties of the rare-earth doped iron-cuprate FeSr2Y2-xCexCu2O10−δ with x = 0.3 and compared the results with previous measurements on a less hole doped sample with x = 0.7. We find that there is a spin-glass and the spin-glass temperature (~23 K) has not changed with hole doping from x = 0.7 to x = 0.3. The conduction mechanism is not affected by hole doping and it is still variable range hopping (VRH) for x = 0.3, which indicates that there is still considerable disorder from Cu and Fe antisite disorder as well as oxygen site disorder in the FeO2-x planes. A large negative magnetoresistance of up to −10% is observed at 8 T but it is less than half of that reported for x = 0.7. The negative magnetoresistance can be accounted using the Nguen, Spivak, and Shklovskii (NSS) model where there is VRH quantum interference. The positive magnetoresistance at 2 K reported for x = 0.7 is not seen in x = 0.3 although the magnetoresistance becomes less negative below 5 K. A positive low temperature magnetoresistance can occur owing to scattering from free localised spins that is not accounted for in the NSS model and the difference in the low temperature magnetoresistance may be owing to a reduced concentration of localised free spins for x = 0.3 when compared with x = 0.7.