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

Abstract

Ultrathin films of Ni–Mn–In with thickness ranging from 100nm down to 10nm 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 10–80nm Ni–Mn–In thin films. In contrast a signature of martensitic phase along with austenite phase was observed in 100nm 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 30nm. 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=0.114mJ/cc.K was observed for 100nm thin film at 240K 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).