Static and dynamic friction in sliding colloidal monolayers

Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

doi:10.1073/pnas.1213930109

Cited by 99 publications

(117 citation statements)

References 45 publications

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“…Phenomena such as superlubric transition, the effect of commensurability and contact geometry, and kink motion, can thus be investigated even in our proposed magnetic mesoscale system. Similar strategies have been recently proposed, making use of model systems such as ion traps [5,18] and colloidal suspensions [8,24,27], however magnetic domains can provide more freedom and flexibility, their properties being continuously tunable over many orders of magnitude. We will focus here only on FFs with perpendicular anisotropy, i.e., the easy axis of the magnetization is perpendicular to the film surface.…”

Section: Introductionmentioning

confidence: 99%

Microscale Motion Control through Ferromagnetic Films

Benassi

Schwenk

Marioni

et al. 2014

Adv Materials Inter

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Actuation and control of motion in micromechanical systems are technological challenges, since they are accompanied by friction and wear, principal and well-known sources of lifetime reduction. In this theoretical work we propose a non-contact motion control technique based on the introduction of a magnetic interaction, i.e., non-contact magnetic friction. The latter is realized by coating two non-touching sliding bodies with ferromagnetic films. The resulting dynamics is determined by shape, size and ordering of magnetic domains arising in the films below the Curie temperature. We demonstrate that the domain behavior can be tailored by acting on handles like ferromagnetic coating preparation, external magnetic fields and the finite distance between the plates. In this way, motion control can be achieved without mechanical contact. Moreover, we discuss how such handles can disclose a variety of sliding regimes. Finally, we propose how to practically implement the proposed model sliding system.

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Section: Introductionmentioning

confidence: 99%

Microscale Motion Control through Ferromagnetic Films

Benassi

Schwenk

Marioni

et al. 2014

Adv Materials Inter

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“…There are other examples of particles moving over ordered substrates, such as vortices in type-II superconductors with periodic pinning arrays [41][42][43] or colloids placed on optically created periodic substrates 44,58 . In these systems the dynamics is overdamped; however, there can be directional locking effects in which the particles preferentially move along symmetry directions of the underlying substrate as the direction of drive is rotated with respect to the substrate lattice [45][46][47][48][49][50][51][52] .…”

Section: Introductionmentioning

confidence: 99%

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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“…While in the macroscopic world it is generally difficult to realize a perfectly incommensurate interface because of defects, irregularities and temperature, in nanotribology 1,2 there are well-defined nanoscale realizations of incommensurate crystal interfaces, such as graphene and other 2D sheets, 3,4 rare-gas monolayers, 5 and colloid monolayers in an optical lattice. 6,7 The present work is devoted to understand the relative state of pinning of an idealized, yet well defined realization of this type of 2D contact, focusing especially on its evolution under conditions of finite temperature, a question totally unexplored so far.…”

Section: Introductionmentioning

confidence: 99%

Finite-temperature phase diagram and critical point of the Aubry pinned-sliding transition in a two-dimensional monolayer

et al. 2017

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The Aubry unpinned-pinned transition in the sliding of two incommensurate lattices occurs for increasing mutual interaction strength in one dimension (1D) and is of second order at T = 0, turning into a crossover at nonzero temperatures. Yet, real incommensurate lattices come into contact in two dimensions (2D), at finite temperature, generally developing a mutual Novaco-McTague misalignment, conditions in which the existence of a sharp transition is not clear. Using a model inspired by colloid monolayers in an optical lattice as a test 2D case, simulations show a sharp Aubry transition between an unpinned and a pinned phase as a function of corrugation. Unlike 1D, the 2D transition is now of first order, and, importantly, remains well defined at T > 0. It is heavily structural, with a local rotation of moiré pattern domains from the nonzero initial Novaco-McTague equilibrium angle to nearly zero. In the temperature (T ) -corrugation strength (W0) plane, the thermodynamical coexistence line between the unpinned and the pinned phases is strongly oblique, showing that the former has the largest entropy. This first-order Aubry line terminates with a novel critical point T = Tc, marked by a susceptibility peak. The expected static sliding friction upswing between the unpinned and the pinned phase decreases and disappears upon heating from T = 0 to T = Tc. The experimental pursuit of this novel scenario is proposed.

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Static and dynamic friction in sliding colloidal monolayers

Cited by 99 publications

References 45 publications

Microscale Motion Control through Ferromagnetic Films

Microscale Motion Control through Ferromagnetic Films

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

Finite-temperature phase diagram and critical point of the Aubry pinned-sliding transition in a two-dimensional monolayer

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