SPSTM

Spin-polarized scanning tunneling microscopy (SPSTM), sometimes written SPSTM or SP-STM, is a variant of scanning tunneling microscopy that uses a magnetically polarized tip to probe the spin-dependent electronic structure of surfaces with atomic-scale spatial resolution. By exploiting the spin dependence of electron tunneling, SPSTM provides contrast related to magnetic order in addition to the conventional topographic signal.

The technique relies on a spin-polarized tunneling current, which varies with the relative orientation of the tip magnetization and the sample magnetization. Tips are typically coated with ferromagnetic materials such as iron, cobalt, or nickel, and experiments are conducted under ultra-high vacuum, often at cryogenic temperatures, though room-temperature measurements are also reported. In addition to imaging, SPSTM can be combined with spectroscopy to measure spin-resolved differential conductance, providing information about the local spin polarization and spin-resolved density of states.

Applications of SPSTM include imaging magnetic domains, domain walls, and complex spin textures on ferromagnetic, antiferromagnetic, and noncollinear magnetic surfaces. It is widely used to study phenomena such as skyrmions, spin polarization at surfaces, and spin-dependent phenomena in topological materials and oxide interfaces. The technique enables direct real-space visualization of magnetic structures at the atomic scale and can reveal how magnetic order correlates with electronic structure.

Challenges in SPSTM involve maintaining stable, well-characterized magnetic tips, controlling tip magnetization direction, and interpreting contrast, which can arise from multiple intertwined factors such as topography, electronic structure, and spin polarization.