Heat capacity of a MnFe(P,Si,B) compound with first-order magnetic transition

Abstract

The heat capacity of a MnFe(P,Si,B) giant magnetocaloric material is investigated by several calorimetric techniques and first-principles calculations. Semi-adiabatic relaxation calorimetry, commercial heat flow and home-made Peltier cells Differential Scanning Calorimeters (DSC) are used to record the heat capacity both around the magnetic transition at room temperature and at low temperatures. The ferromagnetic first-order transition is characterized by a sharp and intense latent heat peak corresponding to a transition entropy change of ∼2.23 J mol−1 K−1, while the thermal hysteresis of ∼2 K remains moderate. The analysis of the heat capacity over a broad temperature range provides an estimate of several important parameters, such as the electronic density of states (N(EF) ≈ 7.2 states eV−1f.u.−1) at low temperatures or an estimate of the Debye temperature θD ≈ 455 K. Different methods (non-magnetic reference, Debye function, phonons calculations) were used to model the lattice contribution to the heat capacity. While this study highlights the difficulty to disentangle lattice, electronic and magnetic contributions from a single quantity such as the heat capacity, it reveals that the excess entropy (magnetic contribution plus latent heat) is considerably larger than in the parent Fe2P.