Successive electric polarization transitions induced by high magnetic field in the single-crystal antiferromagnet Co2Mo3O8

The polar antiferromagnet ${\mathrm{Co}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ was recently reported as a new multiferroic material exhibiting remarkable second-order magnetoelectric (ME) coupling effect while no other metamagnetic transitions occurred at low magnetic field. Herein, we have investigated the ME phenomena under high magnetic field (up to 60 T) in ${\mathrm{Co}}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ single crystals and observed unique ME response associated with the changes in the hidden magnetic moment on the honeycomb lattice. Two spin-flop transitions are unambiguously defined at ${H}_{c1}\ensuremath{\sim}27\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ and ${H}_{c2}\ensuremath{\sim}31\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ under $H$ along the $c$ axis at 1.7 K, accompanied by two successive colossal changes of electric polarization. The results on the anisotropy of magnetoelectricity as well as the angular-dependent polarization are well consistent with the ME tensor prediction, providing a better approach to understand the evolution of magnetic structures under high magnetic field. Therefore, the hidden magnetic transitions and distinctive magnetoelectricity provide a unique platform on which the ME coupling mechanism in the presence of rich magnetic phase transitions can be explored in this 238 family.