Complex magnetic incommensurability and electronic charge transfer through the ferroelectric transition in multiferroic Co3TeO6

Polarized and unpolarized neutron diffraction has been carried out to investigate the nature of the magnetic structures and transitions in multiferroic Co₃TeO₆. Below TM₁ = 26 K long range order develops which is fully incommensurate in all three crystallographic directions. Below TM₂ = 19.5 K commensurate magnetic peaks develop in the Γ₄ irreducible representation, along with a splitting of the ICM peaks along the h direction. Below TM₃ = 18 K this additional magnetic incommensurability disappears, ferroelectricity develops, a commensurate Γ₃ irreducible representation appears, and the k component of the ICM wave vector disappears. Synchrotron x-ray data demonstrate a significant shift of the electronic charge distribution from the Te ions, which together with the unusually small electric polarization and its strong magnetic field dependence suggest this material is an antiferroelectric. Below TM₄ = 15 K the k component of the ICM structure reappears, along with second-order ICM Bragg peaks, which polarized neutron data demonstrate are magnetic in origin with a small net magnetization.