Hysteresis, latent heat and cycling effects on the magnetocaloric response of (NiMnSi)0.66(Fe2Ge)0.34 alloy

Abstract

In this work, we further analyze the promising magnetocaloric (NiMnSi)0.66(Fe2Ge)0.34 alloy, which presents isothermal entropy change values as large as 29 J kg−1 K−1 for 2 T at room temperature. It undergoes a magnetostructural transition accompanied by large thermal/magnetic hysteresis, which remains up to high magnetic fields (corroborated by the elaboration of an experimental magnetic phase diagram). We illustrate that this huge hysteretic behavior (i.e. different responses when magnetizing or demagnetizing) can lead to erroneous interpretation of the order of the phase transition by applying the conventional Banerjee's criterion or the recently developed field dependence analysis of the magnetocaloric effect. Additionally, the cyclability of the response is characterized, showing that after several measurements the magnetocaloric response is significantly reduced (by ≈ 40%) due to sample breaking. These dependences together with the large latent heat of the transition (15.0 kJ kg−1) lead to relatively small values of the adiabatic temperature change for powdered samples at moderate field changes, reaching around 0.6 K for 1.75 T by direct measurement methods.