A Low Background Magneto-Optic Probe for High Sensitivity SQUID Susceptometer

We present a magneto-optic probe designed for the studies of photoinduced magnetization in the highly sensitive SQUID susceptometer MPMS 3. The apparatus is used to conduct light from an external light source into the sealed sample chamber of the susceptometer and deliver the light stimuli right onto the sample, thus allowing uninterrupted measurement as functions of temperature and field, from 1.8 to 350 K, and in magnetic field up to 7 T. The fiber optic sample holder (FOSH) consists mostly of quartz components in order to minimize magnetic background. With background subtraction, the moment resolution of the FOSH can reach 10^-6 emu range even at full field. Future designs are underway to further reduce the magnetic background of the sample holder.