Intrinsic Nature of Stochastic Domain Wall Pinning Phenomena in Magnetic Nanowire Devices

Abstract

Finite temperature micromagnetic simulations are used to probe stochastic domain wall pinning behaviours in magnetic nanowire devices. By exploring field-induced propagation both below and above the Walker breakdown field it is shown that all experimentally observed phenomena can be comprehensively explained by the influence of thermal perturbations on the domain walls’ magnetisation dynamics. Nanowires with finite edge roughness are also investigated, and these demonstrate how this additional form of disorder couples with thermal perturbations to significantly enhance stochasticity. Cumulatively, these results indicate that stochastic pinning is an intrinsic feature of DW behaviour at finite temperatures, and would not be suppressed even in hypothetical systems where initial DW states and experimental parameters were perfectly defined.

Toward Chirality‐Encoded Domain Wall Logic

“…In real devices, similar variations in dynamics would be produced by thermal perturbations, even for a single well defined applied field. [28] The results above indicate that complex Walker breakdown dynamics can cause the operation of 2-in-1-out junctions to break down. However, much like for the NOT gates, the experimental devices were more reliable than would be anticipated from the complex, dynamical simulations.…”

“…We note that the field amplitude here was primarily used as a handle with which to explore variations in the Walker breakdown dynamics. In real devices, similar variations in dynamics would be produced by thermal perturbations, even for a single well defined applied field …”

“…We attribute these to complex Walker breakdown dynamics, which are capable of flipping the chirality of VDWs. [19][20][21]28] Interestingly, the results of our experiments lay closer to those expected from the quasi-static simulations, than from true dynamical simulations, perhaps suggesting that nanowire edge roughness had an inhibiting effect on the complexity of DW dynamics. [26] However, that the required functionalities could be observed with a good degree of reliability even in systems with low damping is an excellent indicator of the feasibility of chirality-encoded logic schemes.…”

Controlling the stability of both the structure and velocity of domain walls in magnetic nanowires

“…27 Oscillations and stochasticity of the DW internal structure and precessional behavior limit reliability, leading to dynamic transitions and hence instability. [28][29][30] For transverse domain walls (T-DWs), such oscillations are linked with a transformation to vortex (V-DWs)/anti-vortex (AVDWs) domain walls associated with Walker breakdown. 31 Depending on the strength field, the DW propagation shows three different regimes that affects its velocity.…”

“…31 Depending on the strength field, the DW propagation shows three different regimes that affects its velocity. 28,[32][33][34] At low magnetic fields, typically up to 10 Oe, below the Walker breakdown threshold, the steady motion is governed by viscous DW propagation in which the DW mobility is positive.…”