Magnetic phase transition in La0.7Sr0.3MnO3/Ta2O5 ceramic composites

Magnetic phase transition characteristic in La0.7Sr0.3MnO3/Ta2O5 composites with different grain size was investigated in this work. There were double maxima in |dM/dT|–T curves for the composites with grain size in the range of 100–200 nm sintered at relative low temperature for short time, which indicated that two paramagnetic–ferromagnetic (PM–FM) transitions happened. The PM–FM transition temperatures of Tc1 and Tc2 were the contribution of grain boundary and grain, respectively. Tc1 varied with Ta2O5 content and sintering condition, whereas Tc2 remained almost the same value. For the composites with grain size larger than 500 nm sintered at high temperature for long time, single magnetic phase transition behavior was observed.