Oblique-incidence Sagnac interferometric scanning microscope for studying magneto-optic effects of materials at low temperatures

We describe an oblique-incidence zero-area Sagnac interferometric microscope for studying spatial and temperature dependence of magneto-optic (MO) effects in samples under cryogenic conditions. The microscope is capable of independently measuring Kerr effects from three Cartesian components of a magnetization and thus can be used to map out the magnetization vector across the sample. For illustration, we present MO Kerr effect images of magnetic domains at 77 K of a LaCrGe3 crystal terminated with an a–c plane (the plane that contains the lattice a-axis and c-axis). We further present measurements of magnetization in these domains from 90 to 77 K during zero-field cooling and field cooling in an external magnetic field from 20 to 150 Oe. The inherently high sensitivity and the capability of detecting a magnetization without external modulation makes such a Sagnac interferometric microscope particularly useful for studying magnetic effects in novel materials at low temperatures.