On the influence of thermal treatment on strain sensors based on the ferromagnetic shape memory alloy NiMnGa

This paper presents a novel concept for improving the performance of mechanical sensors based on the ferromagnetic shape memory alloy NiMnGa. It is shown that a pseudo-plastic deformation that occurs during sensor operation can be fully reversed by heating the magnetic shape memory (MSM) element above its martensite-to-austenite transition temperature and by subsequently cooling it down to room temperature in a moderate external magnetic bias field. This represents an essential feature for future sensor applications as it eliminates the necessity for a strong magnetic bias field. It can therefore help to miniaturize MSM-based mechanical sensors and even increase their sensitivity. This paper presents an initial proof-of-concept using a custom made test setup.