Magnetic transition and large low-field magnetoresistance near Curie temperature in polycrystalline La2/3A1/3MnO3 (A=Ca,Sr)

By means of electron spin resonance, magnetization, and resistivity measurements, phase separation and a large low-field magnetoresistance (MR) accompanied by a first-order metamagnetic transition in the vicinity of Curie temperature (T-C) were observed in polycrystalline La2/3Ca1/3MnO3, but were not observed in polycrystalline La2/3Sr1/3MnO3. It is obvious that the phase separation and large low-field MR near the T-C are not universal features of the colossal MR materials. By combining the magnetic field dependence of magnetization and resistance, it was suggested that the first-order metamagnetic transition from the paramagnetic to ferromagnetic state induced by a magnetic field should be responsible for the large low-field MR observed in polycrystalline La2/3Ca1/3MnO3. Undoubtedly, this observation is very important for exploring large low-field MR in high temperature, which is necessary for practical application of the colossal magnetoresistance effect. (C) 2003 American Institute of Physics.