Research

Research Topics

Our activities evolve around understanding the transport and response properties of solids which root in spin-orbit interaction and non-collinear magnetism, with particular focus on effects of disorder and non-trivial topology of electronic states in various spaces. The concrete directions of our research lie in ab-initio theory of:

  • spin, anomalous and quantum anomalous Hall effects in metals and insulators
  • the effect of spin-orbit torque in ferromagnets and antiferromagnets
  • spin accumulation and spin pumping
  • topological insulators and metals
  • transport properties of skyrmions and chiral magnets
  • Dzyaloshinskii-Moriya interaction and orbital magnetism
  • topological characterization of solids and magnetization dynamics
  • ballistic transport in nano-scale magnets
  • thermal transport phenomena
  • interaction of matter with laser pulses and optical excitation of magnets
  • orbital magnetism of metals and insulators

Research Highlights

 

Long-range chiral exchange interaction in synthetic antiferromagnets

D.-S. Han, K. Lee, J.-P. Hanke, Y. Mokrousov, K.-W. Kim, W. Yoo, Y. L. W. van Hees, T.-W. Kim, R. Lavrijsen, C.-Y. You, H. J. M. Swagten, M.-H. Jung and M. Kläui,

Nature Materials (2019) https://doi.org/10.1038/s41563-019-0370-z

The exchange interaction governs static and dynamic magnetism. This fundamental interaction comes in two flavours—symmetric and antisymmetric. The symmetric interaction leads to ferro- and antiferromagnetism, and the antisymmetric interaction has attracted significant interest owing to its major role in promoting topologically non-trivial spin textures that promise fast, energy-efficient devices. So far, the antisymmetric exchange interaction has been found to be rather short ranged and limited to a single magnetic layer. Here we report a long-range antisymmetric interlayer exchange interaction in perpendicularly magnetized synthetic antiferromagnets with parallel and antiparallel magnetization alignments. Asymmetric hysteresis loops under an in-plane field reveal a unidirectional and chiral nature of this interaction, which results in canted magnetic structures. We explain our results by considering spin–orbit coupling combined with reduced symmetry in multilayers. Our discovery of a long-range chiral interaction provides an additional handle to engineer magnetic structures and could enable three-dimensional topological structures.

 

Engineering Chiral and Topological Orbital Magnetism of Domain Walls and Skyrmions

F. Lux, F. Freimuth, S. Blügel, Y. Mokrousov

Communications Physics 1, 60 (2018)

Electrons which are slowly moving through chiral magnetic textures can effectively be described as if they where influenced by electromagnetic fields emerging from the real-space topology. This adiabatic viewpoint has been very successful in predicting physical properties of chiral magnets. Here, based on a rigorous quantum-mechanical approach, we unravel the emergence of chiral and topological orbital magnetism in one- and two-dimensional spin systems. We uncover that the quantized orbital magnetism in the adiabatic limit can be understood as a Landau-Peierls response to the emergent magnetic field. Our central result is that the spin-orbit interaction in interfacial skyrmions and domain walls can be used to tune the orbital magnetism over orders of magnitude by merging the real-space topology with the topology in reciprocal space. Our findings point out the route to experimental engineering of orbital properties of chiral spin systems, thereby paving the way to the field of chiral orbitronics.

 

Topological Antiferromagnetic Spintronics

L. Smejkal, Y. Mokrousov, B. Yan, A. H. MacDonald

Nature Physics 14, 242-251 (2018)

The recent demonstrations of electrical manipulation and detection of antiferromagnetic spins have opened up a new chapter in the story of spintronics. Here, we review the emerging research field that is exploring the links between antiferromagnetic spintronics and topological structures in real and momentum space. Active topics include proposals to realize Majorana fermions in antiferromagnetic topological superconductors, to control topological protection and Dirac points by manipulating antiferromagnetic order parameters, and to exploit the anomalous and topological Hall effects of zero-net-moment antiferromagnets. We explain the basic concepts behind these proposals, and discuss potential applications of topological antiferromagnetic spintronics.

Fig. 1