Y-doped La0.7Ca0.3MnO3 manganites exhibiting a large magnetocaloric effect and the crossover of first-order and second-order phase transitions

We prepared orthorhombic La0.7-xYxCa0.3MnO3 samples (x = 0, 0.04, 0.06, and 0.08) by conventional solid-state reaction and then studied their magnetic properties and magnetocaloric (MC) effect based on magnetization versus temperature and magnetic-field measurements, M(T, H). The experimental results revealed that an x increase in La0.7-xYxCa0.3MnO3 reduced the ferromagnetic-paramagnetic transition temperature (T-C) from 260K (for x = 0) to similar to 126K (for x = 0.08). Around the T-C, maximum magnetic-entropy changes for a magnetic-field variation interval H = 50 kOe are about 10.7, 8.5, 7.4, and 5.8 J.kg(-1).K-1 for x = 0, 0.04, 0.06, and 0.08, respectively, corresponding to refrigerant capacities RC = 250-280 J.kg(-1). These values are comparable to those of some conventional MC materials, revealing the applicability of La0.7-xYxCa0.3MnO3 in magnetic refrigeration. Using the Arrott method and scaling hypothesis as analyzing high-field M(H, T) data, and the universal-curve construction of the magnetic entropy change, we found a magnetic-phase separation. While the samples x = 0.0.06 exhibit a first-order magnetic phase transition, x = 0.08 exhibits the crossover of the first-to-second-order phase transformation (with its critical-exponent values close to those expected for the tricritical mean-field theory) and has the presence of ferromagnetic clusters even above the TC. Such the variations in the magnetism and MC effect are related to the changes in structural parameters caused by the Y substitution for La because Y doping does not change the concentration ratio of Mn3+/Mn4+. (C) 2015 AIP Publishing LLC.