Optimal temperature range for determining magnetocaloric magnitudes from heat capacity

The determination of the magnetocaloric magnitudes (specific magnetic entropy change, Δs , and adiabatic temperature change, ΔT ) from heat capacity (c ) measurements requires measurements performed at very low temperatures (∼0 K) or data extrapolation when the low temperature range is unavailable. In this work we analyze the influence on the calculated Δs and ΔT of the usually employed linear extrapolation of c from the initial measured temperature down to 0 K. Numerical simulations have been performed using the Brillouin equation of state, the Debye model and the Fermi electron statistics to reproduce the magnetic, lattice and electronic subsystems, respectively. It is demonstrated that it is not necessary to reach experimentally temperatures very close to 0 K due to the existence of certain starting temperatures of the experiments, the same for Δs and ΔT , that minimize the error of the results. A procedure is proposed to obtain the experimental magnitudes of Δs and ΔT with a minimum error from c data limited in temperature. It has been successfully applied to a GdZn alloy and results are compared to those derived from magnetization measurements.This work was supported by the Spanish MINECO and EU-FEDER (project MAT2013-45165-P and MAT2016-77265-R) and the PAI of the Regional Government of Andalucía. LM Moreno-Ramírez acknowledges a FPU fellowship from the Spanish MECD