MFM is another technique in the long list of SPM microscopies. The MFM senses the stray magnetic field above the surface of a sample. A magnetic tip is brought into close proximity with the surface and a small cantilever is used to detect the force between the tip and the sample. The tip is scanned over the surface to reveal the magnetic domain structure of the sample at up to 50 nm resolution. Little sample preparation is required, but the images are difficult to quantify. The ability to make images of the magnetic domain structure makes MFM complementary with the techniques of Kerr microscopy (see MOKE), SEMPA and PEEM.