Studies on Low-Field and Room-Temperature Magnetoresistance in La_(2/3)(Ca_(1-x)Sr_x)_(1/3)MnO_3 Perovskites

摘要

The polycrystalline perovskites La_(2/3)(Ca_(1-x)Sr_x)_(1/3)MnO_3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were successfully prepared by a modified method of solid-state reactions, in which the ingredient mixture with ethanol as a liquid milling medium to form suspension was milled by high-energy ball milling for 10 h and sintered in air at 1400℃ for 10 h. The microstructure, electrical transport, and low-field magnetoresistance (LFMR) of the perovskites were investigated to study the room-temperature magnetoresistance (RTMR) behavior. The results reveal that the metal-to-insulator transition temperature (T_(MI)) increased with increasing doping level x, and the peak values of the magnetoresistance (MR) near T_(MI) dropped with the more Ca~(2+) substituted. A single-phase La_(2/3)Ca_(1/3)MnO_3 showed T_(MI) at 263 K and the peak MR of 23% in the applied field of 3 kOe near T_(MI). The LFMR effect at room temperature could be obtained by controlling the doping Sr~(2+)-substituted Ca~(2+) level. When x = 0.29, transition temperature (T_(MI)) was 305.30 K, and the MR effect was recorded up to 12.9% at 298.55 K and 3 kOe. Finally, the possible mechanism is discussed.