Magnetic force microscopy (MFM) images the spatial variation of magnetic forces on a sample surface. For MFM, the tip is coated with a ferromagnetic thin film. The system operates in non-contact mode, detecting changes in the resonant frequency of the cantilever induced by the magnetic field's dependence on tip-to-sample separation (See Figure8). MFM can be used to image naturally occurring and deliberately written domain structures in magnetic materials.

Figure 8. MFM maps the magnetic domains of the sample surface.

An image taken with a magnetic tip contains information about both the topography and the magnetic properties of a surface. Which effect dominates depends upon the distance of the tip from the surface, because the interatomic magnetic force persists for greater tip-to-sample separations than the van der Waals force. If the tip is close to the surface, in the region where standard non-contact AFM is operated, the image will be predominantly topographic. As you increase the separation between the tip and the sample, magnetic effects become apparent. Collecting a series of images at different tip heights is one way to separate magnetic from topographic effects.