Effect of Cr addition on the structural, magnetic and mechanical properties of magnetron sputtered Ni-Mn-In ferromagnetic shape memory alloy thin films

The effect of Cr substitution for In on the structural, martensitic phase transformation and mechanical properties of Ni-Mn-In ferromagnetic shape memory alloy (FSMA) thin films was systematically investigated. X-ray diffraction results revealed that the Ni-Mn-In-Cr thin films possessed purely austenitic cubic L2(1) structure at lower content of Cr, whereas higher Cr content, the Ni-Mn-In-Cr thin films exhibited martensitic structure at room temperature. The temperature-dependent magnetization (M-T) and resistance (R-T) results confirmed that the monotonous increase in martensitic transformation temperatures (TM) with the addition of Cr content. Further, the room temperature nanoindentation studies revealed the mechanical properties such as hardness (H), elastic modulus (E), plasticity index (H/E) and resistance to plastic deformation (H-3/E-2) of all the samples. The addition of Cr content significantly enhanced the hardness (28.2 +/- 2.4 GPa) and resistance to plastic deformation H-3/E-2 (0.261) of Ni50.4Mn34.96In13.56Cr1.08 film as compared with pure Ni-Mn-In film. As a result, the appropriate addition of Cr significantly improved the mechanical properties with a decrease in grain size, which could be further attributed to the grain boundary strengthening mechanism. These findings indicate that the Cr-doped Ni-Mn-In FSMA thin films are potential candidates for microelectromechanical systems applications.