Magnetism is an inherently quantum mechanical phenomenon and the primary interaction among the magnetic moments and electron spins is the exchange interaction. Because this relies heavily of the wavefunction overlap of nearby orbital states, the typical range of exchange interactions is within a few atomic spacings. Therefore magnetic properties depend very strongly on the atomic scale structure of materials and their interfaces, as demonstrated empirically through numerous magnetic thin film studies over the years (e.g. MBE growth, MOKE measurement, etc.). However, the actual measurement of magnetic ordering at the atomic scale happened more recently through the pioneering development of spin-polarized scanning tunneling microscopy (SPSTM) by Prof. Roland Wiesendanger and co-workers at the University of Hamburg.
The advent of SPSTM opens the door to exploration and discovery of complex and fascinating magnetic order and spin texture in magnetic and non-magnetic systems. In addition to the exchange interaction, the spins and magnetic moments are influenced by magnetic anisotropy and spin-orbit interaction such as Rashba, Dresselhaus, and Dyaloshinkii-Moriya. This can produce a plethora of magnetic phases such as skyrmion, helical, conical, stripe, etc. which can be directly measured by SPSTM. Beyond these equilibrium states, the system can be driven out of equilibrium in several ways including current-induced spin torque, pulsed magnetic fields, and rf microwave excitation. Probing spin dynamics at the atomic scale has scarcely been explored and represents an exciting new frontier: the coherent dynamics of complex quantum systems at the atomic scale.
We utilize a Createc LT-STM/AFM system for spin-polarized imaging of novel magnetic materials grown by MBE (e.g. skyrmion thin films and multilayers), as described in “Epitaxial Growth …“. In addition, we can deposit adatoms to probe the material properties via electron scattering, and we can position adatoms by atomic manipulation to investigate artificial quantum structures. Notably, the STM system is equipped with a 1 Tesla vector magnet for in-plane and out-of-plane fields and high speed rf connections which enable studies of spin dynamics.
| Science | Surface Science … | Spin-Polarized STM Studies of Magnetism and Spin Texture at the Atomic Scale