Quadratic magnetic rotation of polarization plane of light in antiferromagnetic CaMnGe garnet

A magnetic rotation of the light polarization plane proportional to the square magnetic field strength has been found in the tetragonal antiferromagnetic crystal Ca3Mn2Ge3O12. The dependence of the quadratic magnetic rotation on the orientation of the field in the (001) plane has been studied. It was established that this dependence is described by Φ0 cos 2φ. A maximum specific rotation of 0.43 degree/kOe2 mm at λ = 6328 Å and T = 6 K was observed for a magnetic field oriented along the [100] type axis of the cubic phase of this crystal. It is concluded that the magnetic point group of antiferromagnetic CaMnGe-garnet does not include the pure rotation operation 4z but does include antirotation operation 4z′.