Effect of post-deposition annealing on the structure and physical properties of strained epitaxial Ni$_{\mathrm{1-x}}$Ti$_{\mathrm{1-y}}$O$_{3}$ thin films

Ferroelectrically induced weak ferromagnetism had been predicted in compounds MTiO$_{3}$ (M$=$Fe,Mn,Ni) with the LiNbO$_{3}$-type structure. In order to stabilize this metastable structure by oxide heteroepitaxy, we attempted to grow epitaxial NiTiO$_{3}$ films on Al$_{2}$O$_{3}$, and Fe$_{2}$O$_{3}$/Al$_{2}$O$_{3}$ substrates by pulsed laser deposition. Given the structural imperfections of the as-deposited films arising from the large lattice mismatch, which resulted in weak ferroic ordering, we investigated the effect of post-synthesis annealing on the films' properties. Our structural data from x-ray diffraction and electron microscopy suggest that the crystalline quality of the Ni$_{\mathrm{1-x}}$Ti$_{\mathrm{1-y}}$O$_{3}$ films was greatly improved by annealing the films at 1000 $^{\circ}$C for 8 hours. Our physical property characterization indicates increased ferromagnetism in the films. The specific changes in film structure and magnetic as well as polar properties will be discussed. These results suggest that the ferroic domain properties of the films can be favorably altered by post-synthesis heat treatment.