Strain-dependence of the structure and ferroic properties of epitaxial Ni_1−xTi_1−yO₃ thin films grown on sapphire substrates

Polarization-induced weak ferromagnetism has been predicted a few years back in compounds MTiO₃ (M = Fe, Mn, Ni) (Fennie, 2008). We set out to stabilize this metastable, distorted perovskite structure by growing NiTiO₃ epitaxially on sapphire Al₂O₃ (001) substrate, and to control the polar and magnetic properties via strain. Epitaxial Ni_1−xTi_1−yO₃ films of different Ni/Ti ratios and thicknesses were deposited on Al₂O₃ substrates by pulsed laser deposition at different temperatures, and characterized using several techniques. The effect of film thickness, deposition temperature, and film stoichiometry on lattice strain, film structure, and physical properties was investigated. Our structural data from x-ray diffraction, electron microscopy, and x-ray absorption spectroscopy shows that substrate-induced strain has a marked effect on the structure and crystalline quality of the films. Physical property measurements reveal a dependence of the Néel transition and lattice polarization on strain, and highlight our ability to control the ferroic properties in NiTiO₃ thin films by film stoichiometry and thickness. - Highlights: • NiTiO₃ epitaxial thin films with LiNbO₃-type structure by pulsed laser deposition. • Strain varied by film thickness, stoichiometry, and synthesis temperature. • Systematic study of the effect of strain on film structure and physical properties. • Manipulation of ferroic properties by strain confirmed