PNNL

Abstract

Polarization-induced weak ferromagnetism has been predicted recently in LiNbO3-type MTiO3 (M = Fe, Mn, Ni). While coexisting ferroelectric polarization and ferromagnetism have been demonstrated in this family before, first in bulk FeTiO3, then in thin-film NiTiO3, the coupling of the two order parameters has not been confirmed. Here we report the stabilization of polar, ferromagnetic NiTiO3 by oxide epitaxy on LiNbO3 substrate utilizing tensile strain, and demonstrate the theory-predicted coupling between its polarization and ferromagnetism by x-ray magnetic circular dichroism under applied fields. The experimentally observed direction of ferroic ordering in the film is supported by simulation using phase-field approach. Our work validates symmetry-based criteria and first-principles calculations of the coexistence of ferroelectricity and weak ferromagnetism in MTiO3 transition metal titanates crystallizing in the LiNbO3 structure. It also demonstrates the applicability of epitaxial strain as a viable alternative to high-pressure crystal growth to stabilize metastable materials, and a valuable tuning parameter to simultaneously control two ferroic order parameters to create a multiferroic.