Diameter-independent skyrmion Hall angle observed in chiral magnetic multilayers

Abstract

wordsMagnetic skyrmions are topologically non-trivial nanoscale objects. Their topology, which originates in their chiral domain wall winding, governs their unique response to a motion-inducing force. When subjected to an electrical current, the chiral winding of the spin texture leads to a deflection of the skyrmion trajectory, characterized by an angle with respect to the applied force direction. This skyrmion Hall angle was believed to be skyrmion diameter-dependent. In contrast, our experimental study finds that within the plastic flow regime the skyrmion Hall angle is diameter-independent. At an average velocity of 6 ± 1 m/s the average skyrmion Hall angle was measured to be 9° ± 2°. In fact, in the plastic flow regime, the skyrmion dynamics is dominated by the local energy landscape such as materials defects and the local magnetic configuration.

Plastic flow and the skyrmion Hall effect

“…It is also possible that the skyrmion size dependence emerges only at much higher skyrmion velocities than those studied in ref. 14 , due to the washing out of the pinning effectiveness at high drives similar to what is found for vortices in type-II superconductors 7 . To address these issues, future experiments could be performed with artificially created pinning sites of well-controlled size and geometry, where the skyrmion Hall effect can be studied under a systematic change of the pinning length scale.…”

“…The work in ref. 14 also suggests that although the skyrmion motion in the plastic flow regime is disordered, it is also repeatable due to the static pinning landscape, suggesting that the fluctuations or noise associated with the skyrmion motion could have specific repeatable signatures determined by the underlying disorder which could be of use for skyrmion memory devices.…”

“…One sample, many skyrmion sizes In order to understand how pinning affects individual skyrmions, skyrmion-skyrmion interactions, and the evolution of the skyrmion Hall effect, Zeissler et al 14 examine skyrmions in multilayer systems that are prone to disorder. The key feature of this system is that it permits the coexistence of skyrmions of varied size ranging from 35 to 825 nm in diameter, making it possible to study the size dependence of the skyrmion Hall angle in simultaneous measurements of all of the sizes that are present in the sample.…”

Shear banding, intermittency, jamming, and dynamic phases for skyrmions in inhomogeneous pinning arrays

“…The skyrmion Hall angle is constant in the absence of pinning or disorder, but in the presence of disorder it develops a dependence on drive or velocity, starting at a value of zero just at the depinning threshold and gradually increasing with increasing skyrmion velocity until saturating at high drives to a value close to that found in the clean limit [13][14][15][26][27][28][29][30][31] . Particle based 13,24,26,32,33 and continuum based 15,24,27,30 simulations show that the drive dependence of the skyrmion Hall angle is a result of the skyrmion-pin interactions.…”

Chiral edge currents for ac-driven skyrmions in confined pinning geometries

“…One consequence of a finite Magnus term is that the skyrmions move at an angle with respect to an applied drive that is known as the skyrmion Hall angle [18,19,21]. In the absence of quenched disorder or pinning, the skyrmion Hall angle is constant; however, when quenched disorder is present, the skyrmion Hall angle becomes drive or velocity dependent, starting at a value of nearly zero just above the depinning threshold and approaching the disorder-free limit at higher drives [41][42][43][44][45][46][47][48]. The Magnus force also causes the skyrmions to exhibit cyclotron or spiraling motion when they are in a confining potential or interacting with a pinning site [41,[49][50][51][52][53][54][55][56].…”