Skyrmion Lattice Phases in Thin Film Multilayer

Abstract

Phases of matter are ubiquitous with everyday examples including solids and liquids. In reduced dimensions, particular phases, such as the 2D hexatic phase and corresponding phase transitions occur. A particularly exciting example of 2D ordered systems are skyrmion lattices, where in contrast to previously studied 2D colloid systems, the skyrmion size and density can be tuned by temperature and magnetic fields. This allows for the system to be driven from a liquid phase to the onset of a hexatic phase as deduced from the analysis of the hexagonal order. Using coarse-grained molecular dynamics simulations of soft disks, the skyrmion interaction potentials are determined, and it is found that the simulations are able to reproduce the phase behavior. This shows that not only the static behavior of skyrmions is qualitatively well described in terms of a simple 2D model system but skyrmion lattices are versatile and tunable 2D model systems that allow for studying phases and phase transitions in reduced dimensions.

Commensurability between Element Symmetry and the Number of Skyrmions Governing Skyrmion Diffusion in Confined Geometries

“…[ 34,35 ] and [ 37 ] and were also used in our previous work. [ 14,25 ] We neglect any effects of a nonflat energy landscape, which can be observed in some of the experiments, in our idealized simulations.…”

“…[34,35] and [37] and were also used in our previous work. [14,25] We neglect any effects of a nonflat energy landscape, which can be observed in some of the experiments, in our idealized simulations. As shown in Figure 2b, arrangements with triangular symmetry arise for all investigated numbers of skyrmions.…”

“…[1][2][3][4][5][6][7] They are found to exist over a wide range of temperatures, with critical temperatures for their disappearance ranging from a few K to far above room temperature depending on the system. [8][9][10][11][12][13][14] Owing to their potential small size, dynamics at low driving current, and topological properties, magnetic skyrmions have attracted intense interest in fundamental research, and a wide variety of applications have been proposed based on these attributes. Current-induced skyrmion motion could be used, for example, in racetrack memory, logic devices, and spin-transfer nano-oscillators.…”

Phase transitions and phase coexistence: equilibrium systems versus externally driven or active systems - Some perspectives

“…[88] In the absence of any (effective) attractive interactions between such passive colloidal particles, no phase transitions whatsoever are expected in such a colloidal suspension in equilibrium, apart from entropy-driven crystallization [87] at high densities of the colloids (when the typical distance between the particles is of the order of the colloid diameter) and potentially an intermediate hexatic phase in two-dimensional systems. [89][90][91] However, the situation changes fundamentally when we give the Brownian particles a velocity ṽ i of fixed absolute value v 0 , like in the Vicsek model. The direction [4] © IOP publishing.…”

Constructing coarse-grained skyrmion potentials from experimental data with Iterative Boltzmann Inversion

“…This turns them into attractive candidates for applications in novel devices relying on skyrmion-based logic [15,16], Brownian computing [17,18] and racetrack memory [3,[19][20][21][22]. High density lattice states, in which skyrmions strongly interact with each other, have recently moved into the focus of attention [8,[23][24][25][26]. In contrast to colloids [27][28][29], sizes and density of skyrmions can be adjusted on the fly which makes them ideal model systems to study phase behaviour in two dimensions [30] as demonstrated by the demonstration of hexatic and solid phases in Refs.…”