Effect of substrate on processing of multi-gun sputter deposited, near-stoichiometric Ni2MnGa thin films

Near-stoichiometric Ni2MnGa thin films were sputter deposited with a multi-gun sputter deposition system onto sapphire, silicon dioxide and silicon substrates and exposed to heat treatments in vacuum. The multi-gun setup was proven to be feasible for switching compositions quickly and reliably. Using chemical, morphological, magnetic and structural characterisation methods the effects of the different substrates on the Ni2MnGa film properties as a function of heat treatment temperature were studied: sapphire and silicon dioxide provided a metallurgically inert substrate for Ni2MnGa thin films and resulted in films showing room temperature magnetizations of up to  ~ 350 kA/m and austenitic/martensitic structures upon heat treatments at 700 °C. The highest mechanical stability of Ni2MnGa occurred on sapphire substrates, due to the closest match of the thermal expansion coefficients. Silicon substrates led to silicide formation for heating temperatures of 550 °C and above, leading to the loss of ferromagnetism and the austenite/martensite structure in the films.