Investigation of Microscopic Demagnetization Process Using Magneto-Optical Microscopy

Detailed demagnetization process depending on various external field profiles has been investigated using a magneto-optical Kerr/Faraday microscopy for a Co/Pt multilayer film with a perpendicular magnetic anisotropy. By quantitatively analyzing local magnetic domain structures, we propose that it is possible to define a parameter η, which represents how well the demagnetization has been carried out microscopically. The degree of demagnetization η, defined by a ratio between the final demagnetized image intensity and saturated image intensity, has been experimentally found to significantly reflect the microscopic demagnetization behavior. Dependences of η on the maximum amplitude, decreased step size, and effective sweeping rate of alternating demagnetizing field have been systematically investigated together with a direct microscopic observation of magnetic domain structures.