Thermomagnetic Actuation by Low Hysteresis Metamagnetic Ni-Co-Mn-In Films

Abstract

This work presents a novel actuation mechanism using the large abrupt change of magnetization ΔM in a metamagnetic Ni-Co-Mn-In film during first order phase transformation. Free-standing polycrystalline films of the composition Ni50.4Co3.7Mn32.8In13.1 are fabricated by RF magnetron sputtering on a sacrificial polyvinyl alcohol (PVA) substrate. The film composition is tailored to exhibit an abrupt change of magnetization ΔM of 26 emu/g at 50 mT with narrow hysteresis below 8K well above room temperature. A demonstrator is presented consisting of a polyimide cantilever that carries the film material at the front end. When placed between stationary heat source and heat sink, heat transfer gives rise to thermal self-actuation at a cycling frequency of 2 Hz. Design optimization allows for frequency up-conversion to resonant oscillatory motion at frequencies above 160 Hz.