On estimating the magnetocaloric effect from magnetization measurements

We address various aspects on estimating the magnetocaloric effect from magnetization measurements, and the use of a Maxwell relation in first- and second-order phase transitions, including (a) the use of magnetization as a thermodynamic variable in an inhomogeneous situation (structural or chemical distributions, magnetic domains) and (b) non-equilibrium conditions (irreversibility) on first-order phase transitions, including mixed-phase conditions. We find that the Maxwell equation or any other methods such as area differentiation should be used with caution and not include data out of equilibrium, which can lead to spurious results. The use of methods for modeling the magnetic entropy change of first- and second-order magnetic phase transitions, such as Landau and mean-field theory, can be helpful to better understand the nature of the commonly found anomalous peaks in magnetic entropy change and their physical relevance.