Features of the magnetoelectric properties of BiFeO3 in high magnetic fields

It is shown that the destruction of the cycloidal structure of the magnetic ferroelectric ${\mathrm{BiFeO}}_{\mathrm{3}}$ by a high magnetic field ${\mathrm{(H}}_n\text{≈200\hspace{0.05em}}\mathrm{kOe})$ leads to the onset of a linear magnetoelectric effect and the appearance of a toroidal moment. The proof of the existence of a toroidal moment T in a high magnetic field ${\mathrm{(H>H}}_n)$ is based on the experimental observation that the off-diagonal components of the linear ME effect tensor are asymmetric ${\mathrm{(\alpha }}_{12}{\mathrm{=-\alpha }}_{21}$ for ${L}\Vert {c},$ where L is the antiferromagnetic vector), inasmuch as $T_z{\mathrm{\sim \alpha }}_{12}{\mathrm{-\alpha }}_{21}.$