Zernike Seminar: Mathias Kläui (University of Mainz, Germany) - "Specialized Talk: Skyrmions in Spin-Orbitronics and Orbitronics – novel science and applications in memory & non-conventional computing"
|Where:||Room 5114. 0004 Nijenborgh 4|
In this talk I will firstly provide some more in-depth information on selected topics on antiferromagnets and then I particular discuss the relevance of spin structures for spin transport and spin torques: Novel spintronic devices can play a role in the quest for GreenIT if they are stable and can transport and manipulate spin with low power. Devices have been proposed, where switching by energy-efficient approaches is used to manipulate topological spin structures [1,2].
Firstly, to obtain ultimate stability of states, topological spin structures that emerge due to the Dzyaloshinskii-Moriya interaction (DMI) at structurally asymmetric interfaces, such as chiral domain walls and skyrmions with enhanced topological protection can be used [3-5]. Here we will introduce these spin structures ad we have investigated in detail their dynamics and find that it is governed by the topology of the spin structure . By designing the materials, we can even obtain a skyrmion lattice phase as the ground state . Beyond 2D structures, we recently developed systems with chiral interlayer exchange interactions that lend themselves to the formation of chiral 3D structures .
Secondly, for ultimately efficient spin manipulation, we use spin-orbit torques, that can transfer more than 1ħ per electron by transferring not only spin but also orbital angular momentum. We combine ultimately stable skyrmions with spin orbit torques into a skyrmion racetrack memory device , where the real time imaging of the trajectories allows us to quantify the skyrmion Hall effect . Recently, we determined the possible mechanisms that lead to a dependence of the skyrmion Hall effect on skyrmion velocity . We furthermore use spin-orbit torque induced skyrmion dynamics for non-conventional stochastic computing applications, where we developed skyrmion reshuffler devices  based on skyrmion diffusion, which also reveals the origin of skyrmion pinning . Such diffusion can furthermore be used for Token-based Brownian Computing and Reservoir Computing .
Beyond dynamics excited by spin-orbit torques the next step is to use orbital currents that generate orbital torques . We have demonstrated that with an additional Cu/CuOx layer, the acting torques can be increased by more than a factor 10 . This effect has been interpreted as resulting from an orbital Hall current that is converted to a spin current. Finally, an interfacial Orbital Rashba Edelstein Effect has been found, highlighting that the orbital analogues of both the spin Hall effect and the spin-based Rashba Edelstein or Inverse Spin Galvanic effect exist .
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