THERMAL STABILITY AND MEMORY EFFECT IN Mn(Co,Fe)(Ge,Si) CALORIC ALLOYS

In this work, the temperature memory effect (TME) was evaluated in MnCo_0.8Fe_0.2Ge_0.6Si_0.4 and MnCo_0.97Fe_0.03Ge alloys synthesized by arc-melting, with a view to assessing their potential for caloric applications. The room-temperature mixed martensite–austenite microstructure and its evolution under controlled thermal treatments were characterized by X-ray diffraction (XRD). The martensitic transformation kinetics and TME behavior were systematically investigated using differential scanning calorimetry (DSC) under incomplete thermal cycling.

For the MnCo_0.8Fe_0.2Ge_0.6Si_0.4 composition, repeated thermal cycles between room temperature and 973 K induce microstructural refinement of the martensitic phase and a progressive stabilization of austenite. This evolution leads to a continuous decrease in the martensitic transformation enthalpy. This process results in a loss of thermal response reproducibility and a marked degradation of the reversible TME. These effects indicate limited cycling durability, which is critical for practical caloric device operation.

In contrast, the MnCo_0.97Fe_0.03Ge alloy exhibits a more stable martensitic transformation during cycling, maintaining a reversible TME. Nevertheless, functional recovery depends heavily on thermal history; the temperature needed to restore the relaxed state rises alongside the transformation interruption temperature.

These results define the operational windows and cyclability limits of MnCoGe-based systems. Clarifying such thermal conditioning effects helps establish criteria to improve microstructural stability, a core requirement for developing durable solid-state caloric devices.