Martensitic transformation and large exchange bias in Mn-rich Ni–Mn–Sn thin films on mica substrates

The fabrication of high-quality Heusler alloy films with clear martensitic transformation is a challenging issue in the field of magnetic shape memory alloys. Here, flexible Mn-rich Ni–Mn–Sn (Mn49.9Ni40.4Sn9.7) thin films are successfully synthesized by pulsed laser deposition on mica substrates using Ti as buffer layer. XRD analysis reveals that films exhibit austenitic phase with L21 structure at room temperature. The surface morphology indicates polycrystalline structure of fine grains with size of about 60 nm and smooth surface with roughness of less than 1 nm. The temperature dependent magnetization measurement clearly confirms the existence of first-order martensitic transformation. Exchange bias was observed below 70 K with maximum exchange bias field of 148 Oe at 20 K, which is attributed to the exchange coupling between the coexisting antiferromagnetic and ferromagnetic phases due to the various occupations of Mn atoms.