Incommensurate crystal supercell and polarization flop observed in the magnetoelectric ilmenite MnTiO3

MnTiO3 has been studied for many decades, but it was only in the last few years that its magnetoelectric behavior had been observed. Here, we use neutron scattering on two separately grown single crystals and two powder samples to show the presence of a supercell that breaks R3¯ symmetry. We also present the temperature and field dependence of the dielectric constant and pyroelectric current and show evidence of nonzero off-diagonal magnetoelectric tensor elements (forbidden by R3¯ symmetry) followed by a polarization flop accompanying the spin flop transition at μ0HSF=6.5T. Mössbauer spectroscopy on MnTiO3 gently doped with Fe57 was used to help shed light on the impact of the supercell on the observed behavior. Although the full supercell structure could not be solved at this time due to a lack of visible reflections, the full scope of the results presented here suggest that the role of local spin-lattice coupling in the magnetoelectric properties of MnTiO3 is likely more important than previously thought.