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Spin Transport through Interfaces with Strong Spin-Orbit Interactions

Alexey Kovalev (Physics & Astronomy)

The most familiar transport phenomena are associated with flows of electrons and/or holes and are also accompanied by the transfer of spin, energy and charge. Phonons, on the other hand, mostly carry energy while magnons carry spin and energy. The importance of each transport mechanism strongly depends on the temperature. The spin transport couples to the magnetic order parameter, e.g. by the conservation of angular momentum via the spin transfer torque effect. Thus, dynamics of magnetic spin texture, such as magnetic vortex or skyrmion, can be induced in this manner. Magnetic spin textures can also form emergent states of matter where a skyrmion lattice is a good example. The Investigators will work on various unexplored topics related to the interplay of the spin, energy and charge transport in magnetic, thin-film systems in which transport as well as collective and topological phenomena play an important role. In this setting, the emergent order can be influenced by the transport phenomena and various interesting non-equilibrium effects can take place.The theory will be applied to situations where a spin current through the interface is accompanied by charge or magnon currents, such as Pt-Co-AlOx, YIG-Pt, and Co-Ni-Co layered structures and where a pure spin current flows into a ferromagnetic insulator, e.g. CoFe2O4-Pt or YIG-Pt interfaces.

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The objectives of this study include:
i. To study interplay between transport phenomena and magnetic textures in systems with strong spin-orbit interactions. This will involve application of methods of mesoscopic physics, such as scattering matrix approach in order to address the domain wall motion and magnetization reversal by spin-torques relying on spin-orbit interactions. Manipulation of topological objects, such as magnetic vortices and skyrmions, will be considered. Finite temperature effects in relation to spin torques will also be addressed;
ii. To study manipulation of magnetic textures and ordered states (e.g. skyrmion, domain wall, magnetic vortex) in magnetic (both ferromagnetic and antiferromagnetic) insulators. Here the magnetic texture can couple to the energy current and transport of magnons plays an important role. Diagrammatic microscopic as well as phenomenological descriptions will be attempted here;
iii. To study the region in the proximity of the phase transitions. Increased magnetic fluctuations can have non-trivial effect on various transport phenomena where the interplay with magnetocaloric effect is of particular interest.

The proposed scientific research addresses fundamental theoretical aspects related to phase transitions, dynamic effects, and spin and energy transport in magnetic systems with strong spin-orbit interactions in out-of-equilibrium state. This will both shed a light on a wide range of ongoing experiments as well as motivate further developments in materials science. Such studies could also result in new principles for energy harvesting and information processing. In particular, one could envisage magnetic memories based on Dzyaloshinskii-Moriya magnets, and magnonic logic devices.