Imaging of magnetic surfaces by detection of photothermally modulated stray fields

Images from surfaces of ferro- and ferrimagnetic solids are obtained by photothermal modulation of magnetic properties by a focused laser beam and by measuring the surface stray fields using a sensor coil. The lateral resolution is about 10 µm. The method was applied to a sample consisting of cementite plates in an austenite matrix and to monocrystalline ferrite material for video recording heads. Amplitude and phase images are influenced strongly by external magnetic fields. The signal is increasing slightly as a function of the modulation frequency