Dependence of microstructure and magnetism on deposition temperature in Ni-Co-Mn-Ti all-d Heusler alloy thin films

In this work, Ni-Co-Mn-Ti ferromagnetic shape memory alloy thin films, which consists of all 3d metals, are well prepared by direct-current (DC) double targets magnetron co-sputtering method. The deposition temperature (DT) dependence of microstructure and magnetic properties is studied in these thin films. The elemental compositions of these thin films are almost invariable, while the average grain size increases with the increasing DT. Micro-morphology shows that the crystal grains of films are spherical and homogeneous. For the samples deposited at 523 K and 573 K, an unusual magnetization reversal behavior is observed at ∼342 K and ∼225 K, respectively, in the thermomagnetic curves at the applied field μ0H = 1 T. Meanwhile, the hysteresis loops at ambient temperature demonstrate that in Ni-Co-Mn-Ti thin films the ferromagnetic contribution increases at the expense of diamagnetic one as DT increases. The reasons for these results are discussed.