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

Abstract

We have determined the values of critical exponents of two polycrystalline samples (Nd1−xYx)0.7Sr0.3MnO3 (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 β=0.271 and γ=0.922 for x=0, and β=0.234–0.236 and γ=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 (β=0.25 and γ=1.0). Particularly, the TC of x=0 and 0.07 can be any value in the temperature ranges of 240–255K and 170–278K, respectively, depending on the magnitude of applied magnetic field and determination techniques. Around the TC, studying the MC effect of the samples has revealed a large magnetic-entropy change (ΔSm) up to ∼8J/kgK for the applied field interval ΔH=50kOe, corresponding to refrigerant capacity values of 200–245J/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|ΔSm|/dLnH.