Real-time Hall-effect detection of current-induced magnetization dynamics in ferrimagnets

Measurements of the transverse Hall resistance are widely used to investigate electron transport, magnetization phenomena, and topological quantum states. Owing to the difficulty of probing transient changes of the transverse resistance, the vast majority of Hall effect experiments are carried out in stationary conditions using either dc or ac currents. Here we present an approach to perform time-resolved measurements of the transient Hall resistance during current-pulse injection with sub-nanosecond temporal resolution. We apply this technique to investigate in real-time the magnetization reversal caused by spin-orbit torques in ferrimagnetic GdFeCo dots. Single-shot Hall effect measurements show that the current-induced switching of GdFeCo is widely distributed in time and characterized by significant activation delays, which limit the total switching speed despite the high domain-wall velocity typical of ferrimagnets. Our method applies to a broad range of current-induced phenomena and can be combined with non-electrical excitations to perform pump-probe Hall effect measurements

Study of the velocity plateau of Dzyaloshinskii domain walls

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Asynchronous current induced switching of rare earth and transition metal sublattices in ferrimagnetic alloys

Ferrimagnetic alloys are model systems for understanding the ultrafast magnetization switching in materials with antiferromagnetically-coupled sublattices. Here we investigate the dynamics of the rare-earth and transition-metal sublattices in ferrimagnetic GdFeCo and TbCo dots excited by spin-orbit torques with combined temporal, spatial, and elemental resolution. We observe distinct switching regimes in which the magnetizations of the two sublattices either remain syn-6 chronized throughout the reversal process or switch following different trajectories in time and space. In the latter case, we observe a transient ferromagnetic state that lasts up to 2 ns. The asynchronous switching of the two magnetizations is ascribed to the master-agent dynamics induced by the spin-orbit torques in combination with the weak antiferromagnetic coupling, which depends sensitively on the microstructure of ferrimagnets. A larger antiferromagnetic exchange between the two sublattices leads to faster switching and shorter recovery of the magnetization after a current pulse.We thank M. Baumgartner and C. Murer for fruitful discussions and help with the STXM measurements, and F. Binda for the assistance with the measurements at the vibrating sample magnetometer. We thank R. Erni for collaborating in the analysis of the diffraction measurements. We thank C. Vockenhuber for performing Rutherford backscattering measurements on GdFeCo and TbCo. This research was supported by the Swiss National Science Foundation (grant nos 200020_200465 and PZ00P2-179944) and the Swiss Government Excellence Scholarship (ESKAS no. 2018.0056). The PolLux end station was financed by the German Ministerium für Bildung und Forschung (BMBF) through contracts 05K16WED and 05K19WE2. The work by E.M. and V.R. was supported by the Ministerio de Economía y Competitividad of the Spanish Government (project no. MAT2017-87072-C4-1-P) and by the Consejería de Educación of the Junta de Castilla y Leon (project nos SA299P18 and SA0114P20). We acknowledge the Paul Scherrer Institut, Villigen, Switzerland for provision of synchrotron radiation beamtime at beamline X07DA-PolLux of the Swiss Light Source. We also thank the Helmholtz-Zentrum Berlin for the allocation of synchrotron radiation beamtime at the UE-46 Maxymus beamline

Multidomain Memristive Switching of Pt38Mn62/[Co/Ni](n) Multilayers

We investigate the mechanism of analoglike switching of Pt38Mn62/[Co/Ni] multilayers induced by spin-orbit torques. X-ray photoemission microscopy performed during magnetization reversal driven by current pulses shows that sequential switching of reproducible domain patterns can be achieved. Switching proceeds by domain-wall displacement starting from the edges of blocked ferromagnetic domains, which do not switch for either direction of the current and represent up to 24% of the total ferromagnetic area. The antiferromagnetic Pt38Mn62 layer has a granular texture, with the majority of the domains being smaller than 100 nm, whereas the ferromagnetic domains in Co/Ni are typically larger than 200 nm. The blocked domains and the granular distribution of exchange bias constrain the origin as well as the displacement of the domain walls, thus leading to highly reproducible switching patterns as a function of the applied current pulses. These measurements clarify the origin of the memristive behavior in antiferromagnet-ferromagnet structures and provide clues for further optimization of spin-orbit torque switching and memristivity in these systems.ISSN:2331-701

Spin-orbit torque switching of an antiferromagnetic metallic heterostructure

The ability to represent information using an antiferromagnetic material is attractive for future antiferromagnetic spintronic devices. Previous studies have focussed on the utilization of antiferromagnetic materials with biaxial magnetic anisotropy for electrical manipulation. A practical realization of these antiferromagnetic devices is limited by the requirement of material-specific constraints. Here, we demonstrate current-induced switching in a polycrystalline PtMn/Pt metallic heterostructure. A comparison of electrical transport measurements in PtMn with and without the Pt layer, corroborated by x-ray imaging, reveals reversible switching of the thermally-stable antiferromagnetic Néel vector by spin-orbit torques. The presented results demonstrate the potential of polycrystalline metals for antiferromagnetic spintronics. © 2020, The Author(s).ISSN:2041-172

Large voltage tuning of Dzyalonshinskii-Moriya interaction: towards a chirality switch?

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