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

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 magneto-structural 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 approximate to 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.

Automated summary

The study found that the (NiMnSi)(0.66)(Fe2Ge)(0.34) alloy has promising magnetocaloric potential, with isothermal entropy change values as large as 29 J kg(-1) K-1 for 2 T at room temperature. However, sample breakage can significantly reduce the magnetocaloric response by approximately 40%, and the large hysteric behavior may lead to incorrect interpretation of the phase transition order.