A μsR study of the magnetoresistive ruthenocuprates RuSr ₂Nd_1.8-xY_0.2Ce_xCu₂O _10-δ (x=0.95 and 0.80)

Zero field muon spin relaxation (ZF-SR) has been used to study the magnetic properties of the underdoped giant magnetoresistive ruthenocuprates RuSr ₂Nd_1.8-xY_0.2Ce_xCu₂O _10-δ (x=0.95, 0.80). The magnetoresistance (MR) is defined so that MR=((_H0)/₀) and the giant magnetoresistive ruthenocuprates RuSr₂Nd_1.8-xY_0.2Ce _xCu₂O_10-δ exhibit a large reduction in electronic resistivity upon application of a magnetic field. The ZF-SR results show a gradual loss of initial asymmetry A₀ at the ruthenium spin transition temperature, T_Ru. At the same time the electronic relaxation rate, , 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 4K which suggests a relation between Cu spin cluster size and |MR|.