Spin-polarized scanning tunnelling microscopy

The recent experimental progress in spin-polarized scanning tunnelling microscopy (SP-STM)-a magnetically sensitive imaging technique with ultra-high resolution-is reviewed. The basics of spin-polarized electron tunnelling are introduced as they have been investigated in planar tunnel junctions for different electrode materials, i.e. superconductors, optically excited GaAs, and ferromagnets. It is shown that ferromagnets and antiferromagnets are suitable tip materials for the realization of SP-STM. Possible tip designs and modes of operations are discussed for both classes of materials. The results of recent spatially resolved measurements as performed with different magnetic probe tips and using different modes of operation are reviewed and discussed in terms of applicability to surfaces, thin films, and nanoparticles. The limits of spatial resolution, and the impact of an external magnetic field on the imaging process are debated.