Cr2O3 is the archetypal magnetoelectric (ME) material, which has a linear coupling between electric and magnetic polarizations. Quadratic ME effects are forbidden for the magnetic point group of Cr2O3, due to space-time inversion symmetry. In Cr2O3 films grown by sputtering, we find a signature of a quadratic ME effect that is not found in bulk single crystals. We use Raman spectroscopy and magetization measurements to deduce the removal of space-time symmetry, and corroborate the emergence of the quadratic ME effect. We propose that meta-stable site-selective trace dopants remove the space, time, and space-time inversion symmetries from the original magnetic point group of bulk Cr2O3. We include the quadratic ME effect in a model describing the switching process during ME field cooling, and estimate the effective quadratic susceptibility value. The quadratic magnetoelectric effect in a uniaxial antiferromagnet is promising for multifunctional antiferromagnetic and magnetoelectric devices that can incorporate optical, strain-induced, and multiferroic effects.
@article{arxiv.2109.07677,
title = {Quadratic magnetoelectric effect during field cooling in sputter grown Cr$_2$O$_3$ films},
author = {Muftah Al-Mahdawi and Tomohiro Nozaki and Mikihiko Oogane and Hiroshi Imamura and Yasuo Ando and Masashi Sahashi},
journal= {arXiv preprint arXiv:2109.07677},
year = {2021}
}