The tetragonal copper oxide Bi2CuO4 has an unusual crystal structure with a three-dimensional network of well separated CuO4 plaquettes. This material was recently predicted to host electronic excitations with an unconventional spectrum and the spin structure of its magnetically ordered state appearing at TN∼43 K remains controversial. Here we present the results of detailed studies of specific heat, magnetic and dielectric properties of Bi2CuO4 single crystals grown by the floating zone technique, combined with the polarized neutron scattering and high-resolution X-ray measurements. Our polarized neutron scattering data show Cu spins are parallel to the ab plane. Below the onset of the long range antiferromagnetic ordering we observe an electric polarization induced by an applied magnetic field, which indicates inversion symmetry breaking by the ordered state of Cu spins. For the magnetic field applied perpendicular to the tetragonal axis, the spin-induced ferroelectricity is explained in terms of the linear magnetoelectric effect that occurs in a metastable magnetic state. A relatively small electric polarization induced by the field parallel to the tetragonal axis may indicate a more complex magnetic ordering in Bi2CuO4.
@article{arxiv.1703.02069,
title = {Magnetically induced Ferroelectricity in Bi$_2$CuO$_4$},
author = {L. Zhao and H. Guo and W. Schmidt and K. Nemkovski and M. Mostovoy and A. C. Komarek},
journal= {arXiv preprint arXiv:1703.02069},
year = {2017}
}