A beam of electrons is swept across the sample surface as in a standard SEM. When the electron beam strikes a magnetised surface, the secondary electrons emitted from the surface are spin polarised. The polarisation of these electrons can be detected with a spin polarisation detector such as the Mott detector. Images of the magnetic domain structure of the sample can be obtained. Hence the technique is complementary to Kerr microscopy (see MOKE), MFM and PEEM.