Stochastic Processes in Magnetization Reversal Involving Domain-Wall Motion in Magnetic Memory Elements

Bouquin, Paul; Kim, Joo-Von; Bultynck, Olivier; Rao, Siddharth; Couet, S.; Kar, Gouri Sankar; Devolder, T.

doi:10.1103/physrevapplied.15.024037

Cited by 9 publications

(6 citation statements)

References 29 publications

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“…In this paper, we study part of this problem: we let aside the nucleation phenomenon and focus on the subsequent dynamics of a domain wall placed in a circular magnet and then submitted to STT. We expand a recent study [23] where we evidenced that stochastic processes in wall motion were inducing counterintuitive temporal pinning of the wall near the disc center with a strong oscillatory character. These features were also reported independently in a modeling paper [24].…”

Section: Introductionsupporting

confidence: 71%

“…33), the DEVice OptimaL DiametER (DE-VOLDER) for which the retention pond disappears. For this specific diameter, we predict that the wall shall cross the disc center in a ballistic manner independently of its tilt such that the time needed for a domain wall to sweep through the disc will get largely independent from its tilt [23]. This is expected to maximize the reproducibility of the wall dynamics, which is of great interest for magnetic memory applications.…”

Section: B Domain Wall Dynamics At Different Voltagesmentioning

confidence: 99%

“…In this transient process, there is a back-and-forth transfer of energy between the position degree of freedom of the wall and the Néel/Bloch degree of freedom of the wall: U el and U N B,φ act as communicating vessels. This zone of the {q, φ} space in which the wall is transiently stuck is a "retention pond" [23], written P and illustrated as the red contour from labels 1 to 4 in Fig. 10(b).…”

Section: A Preamble: Evolution Of An Hypothetical Central Néel Wallmentioning

confidence: 99%

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Spin-torque induced wall motion in perpendicularly magnetized discs: ballistic versus oscillatory behavior

Bouquin,

Kim,

Bultynck

et al. 2021

Preprint

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We use time-resolved measurement and modeling to study the spin-torque induced motion of a domain wall in perpendicular anisotropy magnets. In disc of diameters between 70 and 100 nm, the wall drifts across the disc with pronounced back-and-forth oscillations that arise because the wall moves in the Walker regime. Several switching paths occur stochastically and lead to distinct switching durations. The wall can cross the disc center either in a ballistic manner or with variably marked oscillations before and after the crossing. The crossing of the center can even occur multiple times if a vertical Bloch line nucleates within the wall. The wall motion is analyzed using a collective coordinate model parametrized by the wall position q and the tilt φ of its in-plane magnetization projection. The dynamics results from the stretch field, which describes the affinity of the wall to reduce its length and the wall stiffness field describing the wall tendency to reduce dipolar energy by rotating its tilt. The wall oscillations result from the continuous exchange of energy between to the two degrees of freedom q and φ. The stochasticity of the wall dynamics can be understood from the concept of the retention pond: a region in the q − φ space in which walls are transiently bound to the disc center. Walls having trajectories close to the pond must circumvent it and therefore have longer propagation times. The retention pond disappears for a disc diameter of typically 40 nm: the wall then moves in a ballistic manner irrespective of the dynamics of its tilt. The propagation time is then robust against fluctuations hence reproducible.

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Section: Introductionsupporting

confidence: 71%

Section: B Domain Wall Dynamics At Different Voltagesmentioning

confidence: 99%

Section: A Preamble: Evolution Of An Hypothetical Central Néel Wallmentioning

confidence: 99%

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Spin-torque induced wall motion in perpendicularly magnetized discs: ballistic versus oscillatory behavior

Bouquin,

Kim,

Bultynck

et al. 2021

Preprint

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“…A separate study of magnetization reversal on magnetic disks, based on the stochastic motion of a domain wall [73,74], uses the wall position and the wall's tilt (i.e., the in-plane orientation at the center wall) to analyze magnetization reversal. This work compares results from micromagnetic simulations at room temperature to key features of the deterministic, reduced-dimensional model, and is able to predict whether the reversal occurs with a single sweep of the domain wall, or whether the wall oscillates as it crosses the center of the disk.…”

Section: Applicationsmentioning

confidence: 99%

Thermally Activated Transitions Between Micromagnetic States

Chaves-O'Flynn¹,

Stein²

2022

Preprint

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We review work by the authors on thermal activation in nanoscopic magnetic systems. These systems present unique difficulties in analyzing noise-induced escape over a barrier, including the presence of nonlocal interactions, nongradient terms in the energy functional, and dynamical textures as initial or saddle states. We begin with a discussion of magnetic reversal between single-domain configurations of the magnetization. Here the transition (saddle) state can be either a single-domain or a spatially varying (instanton-like) configuration, and depending on the system parameters can exhibit either Arrhenius or non-Arrhenius reversal rates. We then turn to a discussion of transitions between magnetic textures, which can be either static and topologically protected or dynamic and not topologically protected. An example of the latter case is the droplet soliton, a rotating nontopologically-protected configuration, which we find can occur either as a metastable or transition state in a nanoscopic magnetic system. After discussing various issues in calculating transition rates, we present results for the activation barriers for creation and annihilation of these magnetic textures. We conclude with a discussion of activated transitions between topologically protected skyrmion textures and other configurations, on which work is ongoing.

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“…Although the switching can be described theoretically by macrospin models [9 and 10], the magnetization reversal caused by STT and SOT is in general a complex and non-uniform process that involves the nucleation and expansion of magnetic domains [11 and 12]. This mechanism prevails over the pure macrospin dynamics even in devices as small as few tens of nm because it is more energetically favorable than the coherent rotation of all the magnetic moments [13][14][15][16]. Time-resolved measurements in magnetic tunnel junctions [16][17][18][19][20] and Hall crosses [21] have revealed that the non-uniform switching comprises two phases at the ns and sub-ns timescale: an initial waiting time t 0 during which the magnetization is at rest and the actual transition of duration ∆t.…”

Section: Introductionmentioning

confidence: 99%

Deterministic and stochastic aspects of current-induced magnetization reversal in perpendicular nanomagnets

et al. 2023

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We study the incubation and transition times that characterize the magnetization switching induced by spin-orbit torques in nanomagnets with perpendicular anisotropy. We present a phenomenological model to interpret the dependence of the incubation time on the amplitude of the voltage pulse and assisting magnetic field, and estimate the volume of the seed domain that triggers the switching. Our measurements evidence a correlation between the incubation and transition times that is mediated by the temperature variation during the electric pulse. In addition, we discuss the stochastic distributions of the two times in terms of the energy barriers opposing the nucleation and expansion of the seed domain. We propose two models based on the log-normal and gamma functions to account for the different origin of the variability of the incubation and transition times, which are associated with a single nucleation barrier and multiple pinning sites, respectively.

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Stochastic Processes in Magnetization Reversal Involving Domain-Wall Motion in Magnetic Memory Elements

Cited by 9 publications

References 29 publications

Spin-torque induced wall motion in perpendicularly magnetized discs: ballistic versus oscillatory behavior

Spin-torque induced wall motion in perpendicularly magnetized discs: ballistic versus oscillatory behavior

Thermally Activated Transitions Between Micromagnetic States

Deterministic and stochastic aspects of current-induced magnetization reversal in perpendicular nanomagnets

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