Spin Transfer Torques in MnSi at Ultralow Current Densities

Jonietz, Florian; Mühlbauer, S.; Pfleiderer, C.; Neubauer, Andreas; Münzer, W.; Bauer, Andreas; Adams, Terry R.; Georgii, R.; Böni, P.; Duine, R. A.; Everschor, Karin; Garst, Markus; Rosch, Achim

doi:10.1126/science.1195709

Cited by 1,174 publications

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“…It was experimentally demonstrated that ultralow current density of B10 5 -10 6 A m À 2 , orders of magnitude smaller than the current density typically used for the domain-wall manipulation, can drive translational and rotational motions of SkX domains in MnSi (ref. 18) and FeGe (ref. 19).…”

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confidence: 99%

Universal current-velocity relation of skyrmion motion in chiral magnets

2013

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Current-driven motion of the magnetic domain wall in ferromagnets is attracting intense attention because of potential applications such as racetrack memory. There, the critical current density to drive the motion is B10 9 -10 12 A m À 2 . The skyrmions recently discovered in chiral magnets have much smaller critical current density of B10 5 -10 6 A m À 2 , but the microscopic mechanism is not yet explored. Here we present a numerical simulation of Landau-Lifshitz-Gilbert equation, which reveals a remarkably robust and universal currentvelocity relation of the skyrmion motion driven by the spin-transfer-torque unaffected by either impurities or nonadiabatic effect in sharp contrast to the case of domain wall or spin helix. Simulation results are analysed using a theory based on Thiele's equation, and it is concluded that this behaviour is due to the Magnus force and flexible shape-deformation of individual skyrmions and skyrmion crystal, which enable them to avoid pinning centres.

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confidence: 99%

Universal current-velocity relation of skyrmion motion in chiral magnets

2013

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“…These topologically protected properties, together with their nanoscale dimensions (10 ~ 100 nm) and ultralow threshold for current-driven motion (10 5 ~ 10 6 Am -2 ) [17][18][19] , make the magnetic skyrmions be promising materials for technological applications in spincronic devices [20] .…”

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A Centrosymmetric Hexagonal Magnet with Superstable Biskyrmion Magnetic Nanodomains in a Wide Temperature Range of 100–340 K

et al. 2016

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Magnetic skyrmions are topologically protected vortex-like nanometric spin textures that have recently received growingly attention for their potential applications in future highperformance spintronic devices. Such unique mangetic naondomains have been recently discovered in bulk chiral magnetic materials, such as MnSi [1][2][3][4] , FeGe [5,6] , FeCoSi [7] , Cu 2 OSeO 3 [8][9][10] , -Mn-type Co-Zn-Mn [11] , and also GaV 4 S 8[12] a polar magnet. The crystal structure of these materials is cubic and lack of centrosymmetry, leading to the existence of Dzyaloshinskii-Moriya (DM) interactions. Unlike the conventional spin configurations, such as helical or conical, that are usually found in chiral magnets, a magnetic skyrmion has a particle-like swirling-spin configuration characterized by a topological index called the skyrmion number [13,14] . The nontrivial topology of magnetic skyrmions results in a number of

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“…In bulk samples, skyrmions form three-dimensional (3D) line objects and occur in a limited range of fields and temperatures 2,16 , while for thin samples the skyrmions exhibit two-dimensional (2D) properties and are stable over a much larger range of fields and temperatures extending close to room temperature [4][5][6][7] . Skyrmions can be set into motion through the application of an external current 7,10,[18][19][20] , and it has been shown that there is a critical current above which the skyrmions depin into a sliding state [19][20][21][22][23][24][25][26] . Skyrmion motion can be directly observed with Lorentz microscopy 7,10 or deduced from changes in the transport properties, permitting the construction of effective skyrmion velocity versus applied force curves that show that the skyrmion velocity increases with increasing current 20 .…”

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Quantized transport for a skyrmion moving on a two-dimensional periodic substrate

2015

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We examine the dynamics of a skyrmion moving over a two-dimensional periodic substrate utilizing simulations of a particle-based skyrmion model. We specifically examine the role of the non-dissipative Magnus term on the driven motion and the resulting skyrmion velocity-force curves. In the overdamped limit, there is a depinning transition into a sliding state in which the skyrmion moves in the same direction as the external drive. When there is a finite Magnus component in the equation of motion, a skyrmion in the absence of a substrate moves at an angle with respect to the direction of the external driving force. When a periodic substrate is added, the direction of motion or Hall angle of the skyrmion is dependent on the amplitude of the external drive, only approaching the substrate-free limit for higher drives. Due to the underlying symmetry of the substrate the direction of skyrmion motion does not change continuously as a function of drive, but rather forms a series of discrete steps corresponding to integer or rational ratios of the velocity components perpendicular ( V ⊥ ) and parallel ( V || ) to the external drive direction: V ⊥ / V || = n/m, where n and m are integers. The skyrmion passes through a series of directional locking phases in which the motion is locked to certain symmetry directions of the substrate for fixed intervals of the drive amplitude. Within a given directionally locked phase, the Hall angle remains constant and the skyrmion moves in an orderly fashion through the sample. Signatures of the transitions into and out of these locked phases take the form of pronounced cusps in the skyrmion velocity versus force curves, as well as regions of negative differential mobility in which the net skyrmion velocity decreases with increasing external driving force. The number of steps in the transport curve increases when the relative strength of the Magnus term is increased. We also observe an overshoot phenomena in the directional locking, where the skyrmion motion can lock to a Hall angle greater than the clean limit value and then jump back to the lower value at higher drives. The skyrmion-substrate interactions can also produce a skyrmion acceleration effect in which, due to the non-dissipative dynamics, the skyrmion velocity exceeds the value expected to be produced by the external drive. We find that these effects are robust for different types of periodic substrates. Using a simple model for a skyrmion interacting with a single pinning site, we can capture the behavior of the change in the Hall angle with increasing external drive. When the skyrmion moves through the pinning site, its trajectory exhibits a side step phenomenon since the Magnus term induces a curvature in the skyrmion orbit. As the drive increases, this curvature is reduced and the side step effect is also reduced. Increasing the strength of the Magnus term reduces the range of impact parameters over which the skyrmion can be captured by a pinning site, which is one of the reasons that strong Magnus force effects reduce the...

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Spin Transfer Torques in MnSi at Ultralow Current Densities

Cited by 1,174 publications

References 30 publications

Universal current-velocity relation of skyrmion motion in chiral magnets

Universal current-velocity relation of skyrmion motion in chiral magnets

A Centrosymmetric Hexagonal Magnet with Superstable Biskyrmion Magnetic Nanodomains in a Wide Temperature Range of 100–340 K

Quantized transport for a skyrmion moving on a two-dimensional periodic substrate

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