Christian Back

Functional Spin Systems

Technical University Munich

Department of Physics

James-Franck-Str. 1

85748 Garching

Tel. +49 89 289 12401


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Research focus: magnetization dynamics, topological quantum materials, hybrid spin-orbit field controlled materials, nanotechnology

The research of our group is focused on the detailed understanding of magnetization dynamics in specially designed ultra thin magnetic layers, in topological materials and at interfaces inducing spin-orbit interaction. We tailor novel hybrid magnetic structures and investigate their static and dynamic magnetic properties. Among the subjects covered in our research are the dynamics in confined magnetic systems, magnonics, spinorbitronics, hybrid topological materials, high resolution magnetic microscopy as well as magnetic phase transitions in low dimensional systems.

In our group we use several techniques to examine magnetization dynamics, the propagation of spinwaves and the efficiency of charge to spin current conversion. At the heart of our research projects are various time and spatially resolved high resolution magnetic microscopy techniques in combination with microwave excitation and detection.

Complex spin structures in topological materials

Hybrid topological materials comprising e.g. of 3D topological insulators (TIs) and ultra thin magnetic layers (ML) promise highly efficient spin to charge conversion due the perfect spin momentum locking of the 2D helical surface states. Consequently these materials are of high relevance for the spintronics community. The topologically protected surfaces states forming at the interface between the TI and a topologically trivial magnetic material (metallic or insulating) are protected from direct backscattering by time reversal symmetry. When a pure spin current is injected from the magnetic material e.g. by spin pumping, it is expected to be efficiently converted into a charge current. Ultimately, highly efficient switching of the magnetization is expected to be realized in hybrid ML/TI nanostructures excited by short electrical current pulses.

We design and fabricate hybrid ML/TI systems using molecular beam epitaxy and investigate spin momentum locking using spin pumping based techniques.

A second class of topological materials we are interested in are complex skyrmion hosting magnetic materials. Prominent examples are the B20 Silicides FexCo1-xSi and MnSi or the insulating material Cu2OSeO3. In these materials we investigate the decay processes of the topologically protected skyrmion tubes as well as magnon transport.

Selected publications

  • Entropy-limited topological protection of skyrmions, Science Advances 3, e1701704 (2017).
  • Time resolved measurements of the switching trajectory of Pt/Co elements induced by spin-orbit torques, Physics Review Letters 118, 257201 (2017).
  • Dynamical Defects in Rotating Magnetic Skyrmion Lattices, Physics Review Letters 118, 207205 (2017).
  • Snell’s Law for Spin Waves, Physics Review Letters 117, 037204 (2016).
  • Spin Hall effects, Review of Modern Physics 87, 1213 (2015).

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