Micro-compression study of Ni-Fe(Co)-Ga magnetic shape memory alloy for MEMS sensors

Magnetic shape memory alloys (MSMAs) are expected to be implemented into micro actuators and sensors because they have a large magnetic field induced strain combined and high response frequency. On the other hand, when dimensions of metallic materials are reduced from a bulk size to the micrometer scale, the mechanical response would vary along with the dimension change. Therefore, it is important to evaluate the mechanical properties of microscale specimens of shape memory alloys to be implemented in miniaturized devices. In the present work, the superelastic properties of the single crystal of Ni
₅₀
Fe
₁₉
Co
₄
Ga
₂₇
(at.%) MSMA have been studied by a micro-compression testing. The specimens were micropillars, fabricated by a focus ion beam technique. The compression stress-strain hysteretic dependences show typical superelastic behavior in a wide temperature range alongside a tendency to disappearance of hysteresis near the critical point at about 373K. The temperature shifts the martensitic transformation start stress with a rate of ~1.1 MPa/K, which is similar in value to the bulk alloy. Thus, the studied alloy could retain the superelastic properties, including in a postcritical region, down to microscale.