Giant magnetostriction and nonsaturating electric polarization up to 60 T in the polar magnet CaBaCo4 O7

Giant magnetostriction in insulating magnetic materials is highly required for applications but is rarely observed. Here we show that giant magnetostriction (>1500ppm) can be achieved in an insulating transition metal oxide CaBaCo4O7 where the ferrimagnetic ordering at TC∼62K 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 (ΔP∼1.6μC/cm2) in response to the applied magnetic field up to 60 T. Geometric frustration as well as the orbital instability of Co2+/Co3+ 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.