Understanding magnetic force microscopy

Magnetic force microscopy is a new method for imaging ferromagnetic domains with a high lateral resolution (10 nm). The basic tip parameters that have to be taken into account to acheive a quantative image interpretation are given. For the electrochemically etched polycrystalline Fe, Ni and cobalt wires, the tip-apex domain is found to be oriented along the tip axis, because of shape anisotropy. The stray field emerging from the tip apex is comparable to the size of the tip saturation field. The effective domain length L determines the image formation: the force due to magnetization patterns of scales which are large compared to L follow the point-dipole approxiamtion. In the opposite case, a single-pole model is more appropiate. While a Co tip can be treated as an isolated domain for Ni and Fe a net polarization in the tip wire induced by the front apex-domain has to be considered. A new analytical theory provides an overall understanding of the image formation and allows the determination of the magnetic field vector and the estimation of its magnitude from measurements. Graphs, Photomicrographs. 42 ref.--AA