Thin films of the Ni-Mn-Ga ferromagnetic martensites due to a strong coupling of the structural and magnetic degrees of freedom are promising materials to be incorporated in novel sensors, actuators and magnetic MEMS.
In general, because the properties of polycrystalline thin films depend strongly on their microstructure, an important research area is concerned with the control of this microstructure, in particular the texture and internal stresses which develop during deposition and post-deposition annealing processes.
In this work, we the X-ray diffraction facility ANKA-Diff at the ANKA synchrotron source in Karlsruhe to study texture and internal stresses in Ni-Mn-Ga thin films sputter deposited on alumina ceramic. Two series of films of two different compositions consisting of 6 specimens each were fabricated by the magnetron deposition at ambient temperature. Each series of films was designed as the single layers of 0.1; 0.2; 0.4; 0.6; 1.0 and 5.0 micron thickness attached to alumina. Films on substrates were vacuum annealed at 1073 K for 36ks. Diffraction measurements were made at 423K. An in-house made temperature controlled heating unit was designed for this purpose. The selected value of temperature ensured that the films were in the austenitic cubic state. The texture measurements were performed using 2Theta scans at fixed Phi and Chi angles which were varied by the 10 deg. step in a range of 0 to 90 deg.
A drastic change of mutual intensities of 220 and 400 peaks as a function of Chi was found while Phi dependence was much less pronounced. An analysis of the results leads to the conclusion about different degree of {110}-type in-plane texture for the films of different thickness. The thickness dependence of the lattice parameter evidences a different degree of internal elastic stresses developed by the films during cooling after annealing.