  Giant magnetostriction in insulating magnetic materials is highly required
for applications but is rarely observed. Here we show that giant
magnetostriction (> 1500 ppm) can be achieved in an insulating transition metal
oxide CaBaCo4O7 where the ferrimagnetic ordering at TC ~ 62 K is associated
with a huge change in the lattice. Moreover, because this material is
pyroelectric with a non-switchable electric polarization (P), the giant
magnetostriction results in a record-breaking magnetoelectric effect - a
gigantic change of electric polarization (deltaP ~ 1.6 {\mu}C/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 new insights on how to achieve both
giant magnetostriction and pronounced magnetoelectric effect in insulating
transition metal oxides.
