Thermo-magneto-mechanical properties of near stoichiometric Ni2MnGa (Mn &gt Ga) thin films deposited by radio-frequency magnetron sputtering on Si substrate

International audienceNear stoichiometric annealed thin films (1.5 to 3 μm) of Ni2MnGa alloy and whose compositions are such that the Martensitic Transformation Temperatures TM(e/a) are in the range -60 ◦C to 200 ◦ C have been deposited by radio-frequency magnetron sputtering on SiO2/Si substrate. Crystallographic structure characterization such as planar spacing d(i), Thermal Expansion Coefficient CTE andstructural domain size L(i)*, has been realized by X-ray diffraction over a wide temperature range from 25 to 205 ◦C. The mechanical properties such as the Young’s modulus (E) and hardness (HB), have been measured by ultra-nano-indentation tests carried out from ambient temperature to 175 ◦C. SQUID-VSM magnetometer measurements from -263 ◦ C to 127 ◦C provide some magneticcharacteristics: evolution of the magnetization M versus the temperature and the Curie temperature TC. Three diffraction peaks which can be attributed to the tetragonal (NM) or modulated (5 M or 7 M) martensitic structures of polycrystalline films have been identified. At ambient temperature Ta, the calculated planarspacing d(i) associated with at least two diffraction peaks present a linear decreasing with TM(e/a). As a function of the temperature and for the austenitic state only one value of the CTE has been determined. For the martensitic state, two values have been extracted and whose change is close to TM(e/a). No evidentevolution has been observed at the vicinity of the Curie temperature. The Young’ modulus and particularly the hardness are very dependent on the film composition, the temperature and the state of the microstructure. At room temperature HB linearly decreases with TM(e/a). As a function of the increasingtemperature, for the martensitic state, E slightly decreases whereas HB is almost constant. In the austenitic domain, E slightly increases and HB linearly increases with the temperature. A phenomenological model has been proposed. The whole of the annealed films show a ferro-magnetic behavior and from the thermomagnetic curves it has been shown that four distinct states can be observed: para or ferromagnetic austenite and para or ferromagnetic martensite. A transition on the magneti-zation, certainly due to a change of the martensitic crystal structure, occurs at the neighborhood of TC. Me-chanical (HB) and magnetic (M) properties are strongly linked and at Ta it has been shown that M is a linearrease function of HB