Low temperature annealing effects on martensitic transformation and exchange bias behavior of Ni–Mn–Sn free-standing alloy thin films

Abstract

Low temperature annealing (<500 °C) is the key to realizing the novel functionalities of Ni–Mn–Sn alloy thin film for applications in a micro-electro-mechanical systems (MEMS) drive. However, it is very difficult to realize the low temperature annealing of Ni–Mn–Sn thin films, which is limited due to substrate constraints. Herein we report the effects of low temperature annealing on the microstructure, martensitic transformation and exchange bias (EB) behavior of Ni₅₁Mn₃₆Sn₁₃ free-standing alloy thin films. We find that low temperature annealing significantly increases the degree of ordering in the austenite phase, leading to an increase in the martensitic transformation temperature (T_M) and the Curie temperature (T_C) of the austenitic phase. More interestingly, a narrow thermal hysteresis and exchange bias effects can be observed in the Ni₅₁Mn₃₆Sn₁₃ free-standing alloy thin films; EB field (H_E) and coercivity (H_C) increase with an increase in annealing temperature. When the annealing temperature of free-standing films is 673 K, the maximum H_E and H_C are 31.10 Oe and 129.64 Oe, respectively. Our work would enhance the material performance for low temperature annealing applications of Ni–Mn–Sn thin films in MEMS.