Giant magnetostriction and nonsaturating electric polarization up to 60 T in the polar magnet CaBa Co 4 O 7

Giant magnetostriction in insulating magnetic materials is highly required for applications but is rarely observed. Here we show that giant magnetostriction $(g1500\phantom{\rule{0.16em}{0ex}}\mathrm{ppm})$ can be achieved in an insulating transition metal oxide $\mathrm{CaBa}{\mathrm{Co}}_{4}{\mathrm{O}}_{7}$ where the ferrimagnetic ordering at ${T}_{\mathrm{C}}\ensuremath{\sim}62\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ is associated with a huge change in the lattice. Moreover, because this material is pyroelectric with a nonswitchable electric polarization ($P$), the giant magnetostriction results in a pronounced magnetoelectric effect---a huge change of electric polarization $(\mathrm{\ensuremath{\Delta}}P\ensuremath{\sim}1.6\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{C}/\mathrm{c}{\mathrm{m}}^{2})$ in response to the applied magnetic field up to 60 T. Geometric frustration as well as the orbital instability of ${\mathrm{Co}}^{2+}/{\mathrm{Co}}^{3+}$ ions is believed to play a crucial role in the giant magnetostriction. Our study provides insights on how to achieve both giant magnetostriction and pronounced magnetoelectric effect in insulating transition metal oxides.