3D-Ising ferromagnetic characteristics and magnetocaloric study in Pr0.4Eu0.2Sr0.4MnO3 manganite

Abstract

The structure, critical exponents and magnetocaloric effect (MCE) of Pr0.4Eu0.2Sr0.4MnO3 were investigated in detail. A solid state reaction method was used in the preparation phase. Phase purity, structure, size, and crystallinity were investigated using XRD and SEM. The Reitveld refinement of XRD pattern shows that the sample adopts an orthorhombic structure with Pnma space group. Analyzing temperature and field dependences of magnetization around the ferromagnetic–paramagnetic transition reveals the sample undergoing the second-order magnetic phase transition with the critical parameters TC∼238K, β=0.310(3), γ=1.264(1) and δ=4.761(9).The exponents are close to 3D-Ising values. This reflects an existence of ferromagnetic short-range order in our sample. With these values one can scale the magnetization below and above TC following a single equation of state. However, it is noteworthy that the scaling relations are obeyed indicating renormalization of interactions around the TC. Temperature variation in effective exponents βeff and γeff resemble with those for disordered ferromagnet. In the vicinity of TC, the magnetic entropy change ΔS reached maximum values of 2.80 and 5.32J/kgK under magnetic field variations of 2 and 5T, respectively. The field dependence of the magnetic entropy changes are also analyzed, which show power law dependence ΔSMmax≈aμ0Hn at transition temperature. The critical exponent analysis related to magnetocaloric effect is described. Moreover, the temperature dependence of the exponent n for a different magnetic field is also studied. The values of n obey to the Curie Weiss law above the transition temperature. In particularly, n can be related to the critical exponents β, γ and δ at the magnetic transition. We used the scaling hypotheses to scale the magnetic entropy change and heat capacity changes to a single universal curve respectively for Pr0.4Eu0.2Sr0.4MnO3 sample.