Magnetization reversal of a thin polycrystalline cobalt film measured by the magneto-optic Kerr effect (MOKE) technique and field-dependent magnetic force microscopy

Abstract

The magnetic properties of a 100-nm-thick cobalt film, deposited thermally on a glass substrate under high-vacuum conditions, were measured ex situ through the longitudinal magneto-optic Kerr effect (MOKE) technique and through field-dependent magnetic force microscopy (MFM). The MOKE measurements showed that the film had a uniaxial anisotropy in the plane of the sample. Two series of MFM images were measured under the presence of an external magnetic field, applied separately along the easy and hard axes, with magnitudes encompassing positive and negative saturation of the sample magnetization. Each series of images recorded the magnetization reversal clearly, revealing and explaining distinctions between the two reversal processes that correlate well with the macroscopic reversals recorded by the MOKE technique. The reversal of the gray-scale polarity with the change of the applied field from negative saturation to positive saturation suggests the presence of a component to the magnetic force that was related directly to the magnetization of the individual grains. A calculation of the easy-axis MFM gray-scale image differences showed a hysteresis-like behavior that agreed qualitatively with the corresponding measured MOKE hysteresis loops.