Analysis of High-Field-Induced Processes with Enthalpy Release in Martensite–Austenite MnCo(Fe)(GeSi) Alloys: Solving PPMS Artifact and Recovery of Heat Capacity

The relaxation calorimeter option in the commercial Physical Property Measurement System (PPMS) has become widely used. Since its introduction, the capabilities of this technique for specific heat measurements have been critically discussed, particularly to avoid misinterpretation of data near phase transitions. Traditional methods rely on cooling curves after sample excitation, where sharp latent heat contributions during heating lead to clear deviations from the fitting model. However, subtle but extended enthalpy contributions (e.g., strain release) may mask these effects, allowing both heating and cooling curves to be well fitted using the standard PPMS protocol. In this work, we develop a procedure that assumes a constant extra power supplied due to subtle enthalpy contributions, enabling consistent interpretation of both heating and cooling curves. This procedure allows: (1) correction of specific heat measurements; and (2) quantification of the enthalpy involved in the transition. The procedure is applied to a magnetic-field-induced transformation in MnCo(Fe)Ge(Si) alloys. Two samples were studied: a single-phase austenite without any field-induced transition, used as a reference, and a mixed austenite-martensite sample, in which apparent deviations in the conductance of the wires evidence the presence of the anomaly.