Spin-polarized Scanning Tunneling Microscopy (SP-STM)

The topic of non-collinear magnetism in ultrathin films and the advancement of spin-polarized scanning tunneling microscopy have been my main research interests for the past years. The first discovery of a nano-scale magnetic ground state, i.e. one that is neither ferromagnetic nor antiferromagnetic, in an ultrathin film, was enabled by the combination of high spatial resolution and spin sensitivity of spin-polarized scanning tunneling microscopy. In the following years we have discovered a variety of different complex spin textures with this method and the strong collaboration between our experimental group with theory has facilitated an in-depth understanding of several mechanisms that lead to nano-scale non-collinear magnetic order.

Sketch of a magnetic skyrmion, cones resemble atomic magnetic moments.

 
In general, complex magnetic order can occur when different magnetic interactions compete. Driving forces for nano-scale magnetic order include frustration of exchange interactions, higher-order magnetic interactions, and the Dzyaloshinskii-Moriya interactions. The latter one can arise in systems with broken inversion symmetry, such as surfaces and interfaces, and it prefers one rotational sense of magnetization rotation over the other. Competition of Heisenberg exchange and Dzyaloshinskii-Moriya interactions can lead to the formation of magnetic skyrmions which have gained a lot of attention in recent years. They are particle-like knots in the magnetization with a material-specific unique rotational sense, that are envisioned as building blocks for future spintronic devices.

The spins of a skyrmion wrap the unit sphere once.