Magnetocaloric effect and critical behavior in Pr_0.5Sr _0.5MnO₃: An analysis of the validity of the Maxwell relation and the nature of the phase transitions

The Maxwell relation, the Clausius-Clapeyron equation, and a non-iterative method to obtain the critical exponents have been used to characterize the magnetocaloric effect (MCE) and the nature of the phase transitions in Pr _0.5Sr_0.5MnO₃, which undergoes a second-order paramagnetic to ferromagnetic (PM-FM) transition at , and a first-order ferromagnetic to antiferromagnetic (FM-AFM) transition at . We find that around the second-order PM-FM transition, the MCE (as represented by the magnetic entropy change, ΔS_M) can be precisely determined from magnetization measurements using the Maxwell relation. However, around the first-order FM-AFM transition, values of ΔS_M calculated with the Maxwell relation deviate significantly from those calculated by the Clausius-Clapeyron equation at the magnetic field and temperature ranges where a conversion between the AFM and FM phases occurs. A detailed analysis of the critical exponents of the second-order PM-FM transition allows us to correlate the short-range type magnetic interactions with the MCE. Using the Arrott-Noakes equation of state with the appropriate values of the critical exponents, the eld- and temperature-dependent magnetization curves, and hence the curves, have been simulated and compared with experimental data. A good agreement between the experimental and simulated data has been found in the vicinity of the Curie temperature T_C, but a noticeable discrepancy is present for . This discrepancy arises mainly from the coexistence of AFM and FM phases and the presence of ferromagnetic clusters in the AFM matrix.