Deconvolution of overlapping first and second order phase transitions in a NiMnIn Heusler alloy using the scaling laws of the magnetocaloric effect

Magnetocaloric materials with a first order phase transition may exhibit additional thermomagnetic phase transitions in the temperature range of interest due to the second-order magnetic phase transitions of the phases. In the case of Heusler alloys exhibiting magneto-structural transformation (martensitic type), this first-order phase transition is usually accompanied by a temperature dependence of magnetization of the different magnetic structures. The temperature of the martensitic transition in this type of materials can be tuned by altering the composition, making possible a close proximity between this transition and the Curie transitions (second-order type) of the structures. This can result in a tight overlap between the two types of magnetocaloric effects, usually of different signs. In this work, the magnetocaloric response of overlapping first and second-order phase transitions of a Ni48.1Mn36.5In15.4 Heusler alloy has been deconvoluted by applying the scaling laws of the magneto caloric effect. This deconvolution allows the prediction of the magnetocaloric response of the pure first order phase transition, helping to gauge if it is worth synthesizing other alloys of the same family for which the Curie transition would be much more distant. The deconvoluted signal confirms that the anomalous experimental decrease of Siso with increasing the field above similar to 3 T is due to the competing contribution of the overlapping second-order phase transition. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

For Heusler alloys exhibiting magneto-structural transformation, the first-order phase transition accompanied by temperature dependence of magnetization of different structures can be tuned by altering composition to be close to Curie transitions. This close proximity may result in tight overlap between two types of magnetocaloric effects, usually of different signs. Deconvolution of the magnetocaloric response allows prediction of the pure first-order phase transition, with the experimental decrease attributed to competing contributions of overlapping second-order phase transitions.