Seminar experimentelle Physik der kondensierten Materie

Electronic devices based on charge motion have been well-studied and widely used in technological devices. However, the electrons can carry not only charges but also spin and orbital angular momentum. Nonequilibrium spin and orbital currents mediate the transfer of the angular momentum to the neighboring magnetic materials enabling the development of efficient spin orbitronic devices. Decoupling these currents from a flow of electronic charges opens opportunities for the electrical control of the magnetization. In this talk, I will first present the efficient spin torque in the magnetic insulators, including current-driving domain wall motion and the Dzyaloshinskii–Moriya interaction. In the second part of the talk, I will present the orbital torque and orbital Rashba-Edelstein magnetoresistance in the light metal system. The orbital-to-spin conversion plays a crucial role in the orbital torque, and the conversion layer can be ferromagnetic metal itself, 3d, 4f, and 5d non-magnetic metals. Our work indicates the efficient current-induced torque in the insulating system with a lower joule heating, and our results on orbital torques show that the magnitude of the orbital torque can be larger than the spin torque. The results further provide insight into the efficient current-induced torques with orbital current from low-cost, environmentally friendly light metals. Biography Shilei Ding received his B.S. in Physics from Peking University, China in 2016, and he received his Ph.D in Condensed Matter Physics from the School of Physics, Peking University (supervisor: Prof. Jinbo Yang). From 2017-2018 and 2019-2020, he was a guest Ph.D. student in the Lab of Prof. Mathias Kläui at Mainz University, Germany. He is now a Postdoctoral Researcher in the Lab of Prof. Pietro Gambardella at ETH Zurich, Switzerland. His research focuses on nonequilibrium spin and orbital current towards spin orbitronic devices, and he has published more than 30 papers in leading journals, including Physical Review Letters, Nano Letters, Advanced Materials, etc.

Antiferromagnets (AFM) hold significant promise as ideal candidates for high-density and ultrafast memory applications. Electrical manipulation of exchange bias has emerged as an effective solution to integrate AFMs into magnetic memories as active elements. With this motivation, we demonstrate the electrical detection of antiferromagnetism in three-terminal magnetic tunnel junctions (MTJs) via exchange bias. A polarity-dependent switching of the exchange bias, driven by spin-orbit torque, is observed with a switching time as short as 0.6 nanoseconds. By incorporating spin-transfer torque, we achieve a substantial reduction in the critical switching current density for spin-orbit torque, enabling reconfigurable AND/OR logic functionalities within a single device. Utilizing the stable multi-state behavior and auto-reset features of this MTJ, we propose an all-spin spiking neural network with a low recognition error rate. These findings hold potential for advancing high-performance memories and in-memory computing.

Spintronics has emerged as a promising field for the development of energy-efficient magnetic memory and logic devices by controlling spin states in ferromagnets via spin-orbit coupling1,2. Efficient control of magnetization in ferromagnets is crucial for high-performance spintronic devices, and magnons have gained renewed interest as a potential avenue for achieving this goal with reduced Joule heating and minimized power consumption. In pursuit of this objective, Previous efforts have focused on optimizing magnon transport with minimal dissipation under the belief that dissipation hinders efficient magnetization control. In contrast, we present an unconventional approach that harnesses magnon dissipation for magnetization control instead of suppressing it. Our approach involves a heterostructure consisting of a ferromagnetic metal and an antiferromagnetic insulator, exploiting an intrinsic spin current within the ferromagnetic metal3,4. By combining a single ferromagnetic metal with an antiferromagnetic insulator that breaks spin transport symmetry while preserving charge transport symmetry, we achieve significant spin-orbit torques comparable to those observed in non-magnetic metals, enabling magnetization switching. Through systematic experiments and comprehensive analysis, we confirm that our findings arise from magnon dissipation within the AFI rather than external spin sources. These results provide novel insights into the mechanisms of spin current generation and dissipation, opening up new possibilities for developing energy-efficient spintronic devices. Reference 1. Sinova, J. et al. Rev. Mod. Phys. 87, 1213–1260 (2015). 2. Shao, Q. et al. IEEE. Trans. Magn. 57, 1–39 (2021). 3. Hibino, Y. et al. Nat. Commun. 12, 6254 (2021). 4. Wang, W. et al. Nat. Nanotechnol. 14, 819–824 (2019).

The controlled displacement of spin textures as magnetic domain walls (DWs) is at the basis of potential applications to magnetic memory storage, neuromorphic computation... However, DWs are very sensitive to weak pinning defects, which strongly reduce their mobility and produce roughening and stochastic avalanche-like motion. The interplay between weak pinning disorder, DW elasticity, thermal fluctuations and an external drive leads to universal dynamical behaviors also encountered for interfaces in ferroelectrics, contact lines in wetting, bacterial colonies, failure propagation... In this variety of physical systems, the interfaces are expected to present both universal [1] and non-universal (material and temperature) behaviors, which are particularly important to disentangle for understanding the pinning dependent dynamics. In this talk, I will discuss a set of recent studies, which reveal the universal scaling functions accounting for both drive and thermal effects on the depinning and thermally activated creep motion [1] of DWs in thin ferromagnetic films with perpendicular anisotropy. Interestingly a self-consistent phenomenological model describing both the creep and depinning dynamics allows to compare the pinning properties of different materials [2], to address the interaction between DWs and pinning disorder [3] and to analyze the dynamics of other magnetic texture as skyrmions [4]. [1] V. Jeudy et al., Phys. Rev. Lett. 117, 057201 (2016); R. Diaz Pardo et al., Phys. Rev. B 95, 184434 (2017); R. Diaz Pardo et al., Phys. Rev. B 100, 184420 (2019); L. J. Albornoz et al., Phys. Rev. B 110, 024403 (2024) [2] V. Jeudy et al., Phys. Rev. B 98, 054406 (2018) [3] P. Géhanne et al., Phys. Rev. Res. 2, 043134 (2020); C. Balan et al., Appl. Phys. Lett. 122, 162401 (2023) [4] S. Mallick et al., Nat. Commun 15, 8472 (2024)