Non-traditional magneto-optic effects and symmetry of antiferromagnetic states in tetragonal garnet Ca3Mn2Ge3O12

The article presents the results of experimental studies of the anisotropic properties of two unconventional magneto-optical effects: the quadratic magnetic rotation of the plane of polarization of light (quadratic Faraday effect) and the linear magneto-optical effect (magnetic analogue of the electro-optical Pockels effect) in the antiferromagnetic tetragonal garnet crystal Ca3Mn2Ge3O12. The results obtained indicate that the symmetry of the spontaneously emerging antiferromagnetic phase differs from that recognized nowadays. In addition, it was found that when cooling the crystal in a magnetic field applied in a certain direction, it is possible to create a metastable antiferromagnetic state that can exist even in the absence of the field.