Academy Research Fellow Lasse Laurson carries out independent research activities related to dynamical processes in various material science applications. His current research consists mainly of the following focus areas:
Domain wall dynamics in low-dimensional ferromagnets (thin films and nanowires). This activity is pursued via a Helsinki Institute of Physics (HIP) Theory Programme Project Domain wall dynamics which Laurson leads. The research is done in collaboration both locally within Aalto University (e.g. with the NanoSpin group of Prof. Sebastiaan van Dijken) and across Europe, in particular via an associated partnership in the European Commission ITN project WALL, with Laurson the Scientist in Charge of the project at Aalto.
Right: Domain wall (DW) dynamics in a model of in-plane magnetized thin ferromagnetic films with different relative strengths of dipolar interactions (increasing from left to right). The DW morphology (example DW configurations shown in black) evolves from rough to zigzag, and the Barkhausen avalanches (regions with different colours) exhibit a cross-over between two universality classes. See also Phys. Rev. B 89, 104402 (2014).
Left: A domain wall separating two out-of-plane domains in a thin ferromagnetic film, including an internal domain wall (or a Bloch line), separating regions of opposite in-plane magnetisation within the domain wall; magnetisation direction is indicated by the arrows, and the different colours. Our results show how such internal walls can be nucleated and subsequently displaced along the main domain wall by applying magnetic fields or spin-polarised electric currents. We show that due to topological protection of the internal domain wall structure by the surrounding out-of-plane domains, Walker breakdown is absent in the dynamics of the internal walls; this could lead to interesting possibilities to develop spintronics applications where domain walls would serve as guides for fast internal domain wall propagation (Figure: Touko Herranen). See also Phys. Rev B 92, 100405(R) (2015).
Plastic deformation of crystalline solids, or dislocation dynamics, is studied in close collaboration with other members of the CSM group, and with collaborators across Europe. Here, the key questions relate to the character of the “yielding transition”, and to that of the ensuing deformation bursts or avalanches, see e.g. Phys. Rev. Lett. 112, 235501 (2014), and Scientific Reports 5, 10580 (2015).
Friction between two surfaces, with or without a lubricant layer in between. A related Aalto Science InstituteThematic Research Programme Machine learning strategies for optimising frictional properties of materials is about to start during autumn 2014, with Laurson the coordinator of the Programme. The research is also related to a COST network Understanding and Controlling Nano and Mesoscale Friction. For an example of our recent friction research, see e.g. Phys. Rev. Lett. 114, 095502 (2015).
General physics of avalanching systems, with the aim of understanding the fundamental nature of the bursty dynamics encountered in various driven systems (for examples, see above). For such studies, we consider simple minimal models, such as driven elastic interfaces in random media.
Left: The average shape of the activity bursts or avalanches in driven interfaces in random media, with different ranges of the elastic interactions, showing how the average avalanche shape depends on the universality class of the avalanche dynamics. In particular, we find a small temporal asymmetry of the average shapes, evolving with the universality class, and reflecting a broken time-reversal symmetry in the avalanche dynamics, see Nature Communications 4, 2927 (2013).
For more papers, have a look at the list of publications.
Department of Applied Physics
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