Purely magnetization-induced second-harmonic generation in thin garnet films

Optical second-harmonic generation (SHG) of purely magnetic origin has been observed in thin films of Lu3-χ Biχ Fe5-y Gay O12 grown on (100) oriented gadolinium gallium garnet (GGG) substrates for the purpose of magneto-optical imaging. The films have in-plane magnetization, and when studied in transmission at normal incidence all relevant elements of the crystallographic part of the second order non-linear optical susceptibility tensor vanish identically, while a magnetization-induced contribution remains. The observed rotational anisotropy SHG signal in a transverse magnetic field is demonstrated to be indeed of purely magnetic origin, and can be switched off by applying a polar magnetic field.