Critical behavior of Y-doped Nd0.7Sr0.3MnO3 manganites exhibiting the tricritical point and large magnetocaloric effect

We have determined the values of critical exponents of two polycrystalline samples (Nd1-xYx)(0.7)Sr0.3MnO3 (x = 0 and 0.07) from the magnetization data versus temperature and magnetic field, M(H,T), to learn about their magnetic and magnetocaloric (MC) properties. The results reveal the samples exhibiting the crossover of first-order and second-order phase transitions, where the exponent values beta = 0.271 and gamma = 0.922 for x = 0, and beta = 0.234-0.236 and gamma = 1.044-1.063 for x = 0.07 determined by using modified Arrott plots and static-scaling hypothesis are close to those expected for the tricritical mean-field theory (beta = 0.25 and gamma = 1.0). Particularly, the T-c of x = 0 and 0.07 can be any value in the temperature ranges of 240-255 K and 170-278 K, respectively, depending on the magnitude of applied magnetic field and determination techniques. Around the T-c, studying the MC effect of the samples has revealed a large magnetic-entropy change (Delta S-m) up to similar to 8 J/kg K for the applied field interval Delta H = 50 kOe, corresponding to refrigerant capacity values of 200-245 J/kg. These phenomena are related to the crossover nature and the persisting of FM/anti-FM interactions even above the Tc, as further confirmed by electron-spin-resonance data, Curie-Weiss law-based analyses, and an exponential parameter characteristic of magnetic order n = dLn vertical bar Delta S-m vertical bar/dLnH. (C) 2014 Elsevier B.V. All rights reserved.