A mu SR study of the magnetoresistive ruthenocuprates RuSr2Nd1.8-xY0.2CexCu2O10-delta (x=0.95 and 0.80)

Zero field muon spin relaxation (ZF-mu SR) has been used to study the magnetic properties of the underdoped giant magnetoresistive ruthenocuprates RuSr2Nd1.8-xY0.2CexCu2O10-delta (x = 0.95, 0.80). The magnetoresistance (MR) is defined so that MR = ((rho(H) - rho(0))/rho(0)) and the giant magnetoresistive ruthenocuprates RuSr2Nd1.8-xY0.2CexCu2O10-delta exhibit a large reduction in electronic resistivity upon application of a magnetic field. The ZF-mu SR results show a gradual loss of initial asymmetry A(0) at the ruthenium spin transition temperature, T-Ru. At the same time the electronic relaxation rate, lambda, shows a gradual increase with decreasing temperature below T-Ru. These results have been interpreted as evidence for Cu spin cluster formation below T-Ru. These magnetically ordered clusters grow as the temperature is decreased thus causing the initial asymmetry to decrease slowly. Giant magnetoresistance is observed over a wide temperature range in the materials studied and the magnitude increases as the temperature is reduced from T-Ru to 4 K which suggests a relation between Cu spin cluster size and vertical bar - MR vertical bar.