Abstract
Magnetic skyrmions are whirl-like nano-objects with topological protection. When driven by direct currents, skyrmions move but experience a transverse deflection. This so-called skyrmion Hall effect is often regarded a drawback for memory applications. Herein, we show that this unique effect can also be favorable for spintronic applications: We show that in a racetrack with a broken inversion symmetry, the skyrmion Hall effect allows to translate an alternating current into a directed motion along the track, like in a ratchet. We analyze several modes of the ratchet mechanism and show that it is unique for topological magnetic whirls. We elaborate on the fundamental differences compared to the motion of topologically trivial magnetic objects, as well as classical particles driven by periodic forces. Depending on the exact racetrack geometry, the ratchet mechanism can be soft or strict. In the latter case, the skyrmion propagates close to the efficiency maximum.
Highlights
Magnetic skyrmions are whirl-like nano-objects with topological protection
The reason is that the skyrmions follow a soft ratchet mechanism that is distinct from typical classical ratchet mechanisms and not as efficient. We investigate this unique mechanism in more detail and show that it can be turned into a strict and more efficient ratchet mechanism by tweaking the racetrack geometry
We have shown that the skyrmion Hall effect can be utilized to drive topologically non-trivial spin textures by alternating currents (AC) currents, when the racetrack is not mirror-symmetric
Summary
Magnetic skyrmions are whirl-like nano-objects with topological protection. When driven by direct currents, skyrmions move but experience a transverse deflection. A charged particle in a periodic but asymmetric environment, can be driven by an alternating electric field; it will move step-by-step from one energy minimum to the minimum along the direction with the smaller potential gradient This so-called ratchet mechanism has been widely explored, especially for using thermal fluctuations to drive molecular motors[2, 3] or even in spintronics to unidirectionally move magnetic solitons in a shift register[4] or to drive spins with alternating voltages[5, 6]. We consider fundamentally different spin textures: the nano-sized magnetic skyrmions[11,12,13] which are whirl-like magnetic objects that possess particle-like properties Due to the topological charge of the skyrmions, the objects do not move parallel to the applied current but are deflected towards the edge of the racetrack[14, 22,23,24,25,26]
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