Field-free spin-orbit torque switching through domain wall motion

Abstract

Deterministic current-induced spin-orbit torque (SOT) switching of magnetization in a heavy transition metal/ferromagnetic metal/oxide magnetic heterostructure with the ferromagnetic layer being perpendicularly-magnetized typically requires an externally-applied in-plane field to break the switching symmetry. We show that by inserting an in-plane magnetized ferromagnetic layer CoFeB underneath the conventional W/CoFeB/MgO SOT heterostructure, deterministic SOT switching of the perpendicularly-magnetized top CoFeB layer can be realized without the need of in-plane bias field. Kerr imaging study further unveils that the observed switching is mainly dominated by domain nucleation and domain wall motion, which might limit the potentiality of using this type of multilayer stack design for nanoscale SOT-MRAM application. Comparison of the experimental switching behavior with micromagnetic simulations reveals that the deterministic switching in our devices cannot be explained by the stray field contribution of the in-plane magnetized layer, and the roughness-caused Néel coupling effect might play a more important role in achieving the observed field-free deterministic switching. *

Pulse-width and temperature dependence of memristive spin–orbit torque switching

“…By pre-magnetizing the sample with a large positive or negative in-plane external field ( 1000 Oe ± ), the polarity of these two case are opposite (data not shown here). This further confirms the existence of the symmetry-breaking effective field, and the mechanism of achieving field-free SOT switching can be attributed to the interlayer exchange coupling 17,18,32 or the Néel orange-peel effect 19,20 between two FMs.…”

“…5,6 To realize the "field-free" SOT switching, some specific mechanism must be adopted and additional engineering on the layer design is necessary, such as introducing exchange bias, 10,11 wedged structure, [12][13][14][15][16] interlayer exchange coupling, 17,18 or Néel orange-peel effect. 19,20 Presently many of the SOT-related studies focus on enhancing SOT efficiency and realizing deterministic field-free SOT switching through layer stack engineering. However, magnetic heterostructures or devices with good thermal stability is also a key factor to make such memory applications useful.…”

Energy and Performance Benchmarking of a Domain Wall-Magnetic Tunnel Junction Multibit Adder

“…By injecting a current through the input (left) terminal of the device, the DW can be translated along the length of the track. This occurs either by STT applied on the DW by a spin-polarized current through the ferromagnetic track or by a strictly current-induced SOT [23] arising from the spin Hall effect [3], [24] in a heavy metal layer that lies below the track. Fig.…”

Field-free approaches for deterministic spin–orbit torque switching of the perpendicular magnet

“…Meanwhile, the interlayer exchange-coupling is still sufficiently strong to assists field-free switching after replacing the Ru spacer with Pt or slightly modifying the spacer thickness. Murray et al pointed out that the interlayer exchange-coupling can still be achieved without an AFM layer [65]. Reproduced from [90].…”