Low temperature magnetoresistance in the Ru-1222 superconductor

Samples with nominal compositions RuSr2R1.4Ce0.6Cu2O10−δ (R = Eu, Sm) were synthesized and their magnetic and transport properties were investigated. A superconducting transition is observed in the ρ(T) dependencies at Ton = 40 K for R = Eu and 32 K for R = Sm. The χ′(T) dependencies denoted a lack of negative values of χ′ in the temperature range Td < T < Tc, where Td = 15 K for R = Eu and ≈ 6 K for R = Sm. The wide hysteresis in the M(H) dependencies suggests that this feature is connected with a spontaneous vortex phase. A significant magnetoresistive effect was observed for the first time in the Ru-1222 superconductor at T < Tc—up to 750% for the Eu-containing sample and 130% for the Sm-containing one. The nature of the observed magnetoresistance was discussed.