Structure evolution and entropy change of temperature and magnetic field induced magneto-structural transition in Mn_1.1Fe_0.9P _0.76Ge_0.24

The compound Mn_1.1Fe_0.9P_0.76Ge _0.24 has been studied using neutron powder diffraction (NPD), differential scanning calorimeter (DSC), and magnetic measurements, in order to clarify the nature of the magnetic and structural transition and measure the associated entropy change (ΔS). The strongly first order transition occurs from a paramagnetic (PM) to a ferromagnetic (FM) phase and can be induced either by temperature or by an applied magnetic field. Our investigations indicate that the two processes exhibit identical evolutions regarding the crystal and magnetic structures, indicating they should have the same entropy change. We, therefore, conclude that the ΔS_DSC obtained by the DSC method (where the transition is temperature induced) is valid also for the magnetically induced transition, thus avoiding uncertainties connected with the magnetic measurements. We have obtained the ΔS_DSC = 33.8 J/kg · K for this sample upon cooling, which would increase to 42.7 J/kg · K for a impurity-free and completely homogeneous sample. For comparison, the magnetic entropy changes (ΔS_M) induced by magnetic field and calculated using the Maxwell relation yields a ΔS _M = 46.5J/kg · K, 38% higher than ΔS_DSC. These entropy results are compared and discussed.