Thin Solid Films, Vol.662, 47-53, 2018
Controlling the structure and ferroic properties of strained epitaxial NiTiO3 thin films on sapphire by post-deposition annealing
Ferroelectrically induced weak ferromagnetism had been predicted earlier in metal titanate compounds MTiO3 (M = Fe, Mn, Ni) with the lithium niobate-type (LiNbO3) structure. In order to stabilize this metastable structure by oxide heteroepitaxy, we attempted to grow epitaxial nickel titanate (NiTiO3) films on the nonpolar, nonmagnetic sapphire substrate by pulsed laser deposition. As a follow-up to our earlier work, we investigated the effect of post-synthesis annealing in order to improve physical properties. Our structural data from x-ray diffraction and electron microscopy suggest that the crystalline quality of the NiTiO3 films was greatly improved by annealing the films at 600 and 1000 degrees C, with new phase formation along the interface at 1000 degrees C. Our physical property characterization indicates increased ferromagnetism and polarization after 600 degrees C, but a change in the magnetic state to likely ferrimagnetism, and a loss of polarization after the 1000 degrees C treatment. Our results suggest that the ferroic domain properties of the NiTiO3 films can be favorably altered by post-synthesis heat treatment at the proper temperature to manipulate interfacial strain and enhance the multiferroic properties.