Manifestation of martensitic phase transformation and magneto-caloric properties in high quality magnetron sputtered Ni-Mn-In//Si ultra thin films

Ultrathin films of Ni-Mn-In with thickness ranging from 100 nm down to 10 nm deposited on Si (100) were investigated for thickness dependence of martensitic phase transformation and their magnetic properties. X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) revealed the (220) oriented austenitic cubic phase growth of 10-80 nm Ni-Mn-In thin films. In contrast a signature of martensitic phase along with austenite phase was observed in 100 nm sputtered coated Ni-Mn-In thin films. A systematic magnetization versus temperature (M-T) study of Ni-Mn-In thin films implies that martensitic transformation is possible down to 30 nm. It also suggests the reduction in martensitic transformation temperatures (Mf & As) along with an increase in magneto-structural transition temperature course with decreasing film thickness. The magnetocaloric curves evaluated from isothermal magnetization study showed an increase in magnetic entropy change (ΔSm) with increasing film thickness, a maximum attainable ΔSm = 0.114 mJ/cc.K was observed for 100 nm thin film at 240 K as Ni-Mn-In endures a transition from martensitic phase to austenitic phase with a concomitant magnetic ordering. A shift in ΔSm maxima towards higher temperature with increase in film thickness was also observed from magneto-caloric graphs. The R-T measurements performed to investigate the martensitic to austenitic phase transition were in good agreement with thermo-magnetic curves. The tuning of martensitic phase transformation of Ni-Mn-In opens up a new possibility for the wide range working of many spintronics devices like magneto-electric random access memory (MERAM).