Critical behavior and magnetocaloric effect of Pr12xCaxMnO3

The critical behavior of Pr1!xCaxMnO3 samples with x 0.25, 0.27, and 0.29 has been investigated. Detailed analyses of magnetic-field dependences of magnetization at temperatures around the paramagnetic-ferromagnetic transition, M(H, T), reveal that the samples undergo a second-order mag-netic phase transition. The Arrott plot method predicts the values of critical parameters to be TC # 118K, b 0.3516 0.003, c 1.3726 0.002, and d 4.906 0.02 for x 0.25; TC # 116K, b 0.3626 0.002, c 1.1326 0.004, and d 4.096 0.03 for x 0.27; and TC # 110K, b 0.5216 0.002, c 0.9126 0.005, and d 2.716 0.02 for x 0.29. The values of b 0.351 (for x 0.25) and b 0.362 (for x 0.27) are close to the value b 0.365 expected for the 3D Heisenberg model, proving an existence of short-range ferromagnetic interactions in these samples. A slight increase in Ca-doping content (x 0.29) leads to the shift of the b value (0.521) towards that of the mean-field theory (with b 0.5) characteristic of long-range ferromagnetic interactions. The samples also exhibit a magnetocaloric effect: around TC of Pr1!xCaxMnO3 compounds, magnetic-entropy change reaches the maximum values of about 5.0, 4.1, and 2.5 J kg!1 K!1 for x 0.25, 0.27, and 0.29, respectively, under an applied-field change of 50 kOe. Magnetic-field dependences of the maximum magnetic-entropy change (DSmax) obey a power law jDSmax(H)j / Hn, where exponent value