20 research outputs found
Constructing coarse-grained skyrmion potentials from experimental data with Iterative Boltzmann Inversion
In an effort to understand skyrmion behavior on a coarse-grained level, skyrmions are often described as 2D quasiparticles evolving according to the Thiele equation. Interaction potentials are the key missing parameters for predictive modeling of experiments. Here, the Iterative Boltzmann Inversion technique commonly used in soft matter simulations is applied to construct potentials for skyrmion-skyrmion and skyrmion-magnetic material boundary interactions from a single experimental measurement without any prior assumptions of the potential form. It is found that the two interactions are purely repulsive and can be described by an exponential function for micrometer-sized skyrmions in a ferromagnetic thin film multilayer stack. This captures the physics on experimental length and time scales that are of interest for most skyrmion applications and typically inaccessible to atomistic or micromagnetic simulations
Constructing coarse-grained skyrmion potentials from experimental data with Iterative Boltzmann Inversion
In an effort to understand skyrmion behavior on a coarse-grained level, skyrmions are often described as 2D quasiparticles evolving according to the Thiele equation. Interaction potentials are the key missing parameters for predictive modeling of experiments. Here, the Iterative Boltzmann Inversion technique commonly used in soft matter simulations is applied to construct potentials for skyrmion-skyrmion and skyrmion-magnetic material boundary interactions from a single experimental measurement without any prior assumptions of the potential form. It is found that the two interactions are purely repulsive and can be described by an exponential function for micrometer-sized skyrmions in a ferromagnetic thin film multilayer stack. This captures the physics on experimental length and time scales that are of interest for most skyrmion applications and typically inaccessible to atomistic or micromagnetic simulations
Skyrmion Lattice Phases in Thin Film Multilayer
Phases of matter are ubiquitous with everyday examples including solids and
liquids. In reduced dimensions, particular phases, such as the two-dimensional
(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 field. This allows us to drive the system
from a liquid phase to a hexatic phase as deduced from the analysis of the
hexagonal order. Using coarse-grained molecular dynamics simulations of soft
disks, we determine the skyrmion interaction potentials and we find that the
simulations are able to reproduce the full two-dimensional phase behavior. This
shows that not only the static behavior of skyrmions is qualitatively well
described in terms of a simple two-dimensional model system but skyrmion
lattices are versatile and tunable two-dimensional model systems that allow for
studying phases and phase transitions in reduced dimensions.Comment: Corrected Acknowledgement
Faster chiral versus collinear magnetic order recovery after optical excitation revealed by femtosecond XUV scattering
While chiral spin structures stabilized by Dzyaloshinskii-Moriya interaction
(DMI) are candidates as novel information carriers, their dynamics on the fs-ps
timescale is little known. Since with the bulk Heisenberg exchange and the
interfacial DMI two distinct exchange mechanisms are at play, the ultra-fast
dynamics of the chiral order needs to be ascertained and compared to the
dynamics of the conventional collinear order. Using an XUV free-electron laser
we determine the fs-ps temporal evolution of the chiral order in domain walls
in a magnetic thin film sample by an IR pump - X-ray magnetic scattering probe
experiment. Upon demagnetisation we observe that the dichroic (CL-CR) signal
connected with the chiral order correlator in the domain walls
recovers significantly faster than the (CL+CR) sum signal representing the
average collinear domain magnetisation . We explore possible
explanations based on spin structure dynamics and reduced transversal
magnetisation fluctuations inside the domain walls and find that the latter can
explain the experimental data leading to different dynamics for collinear
magnetic order and chiral magnetic order.Comment: 28 pages, 14 figure
Enhanced thermally-activated skyrmion diffusion with tunable effective gyrotropic force
Magnetic skyrmions, topologically-stabilized spin textures that emerge in magnetic systems, have garnered considerable interest due to a variety of electromagnetic responses that are governed by the topology. The topology that creates a microscopic gyrotropic force also causes detrimental effects, such as the skyrmion Hall effect, which is a well-studied phenomenon highlighting the influence of topology on the deterministic dynamics and drift motion. Furthermore, the gyrotropic force is anticipated to have a substantial impact on stochastic diffusive motion; however, the predicted repercussions have yet to be demonstrated, even qualitatively. Here we demonstrate enhanced thermally-activated diffusive motion of skyrmions in a specifically designed synthetic antiferromagnet. Suppressing the effective gyrotropic force by tuning the angular momentum compensation leads to a more than 10 times enhanced diffusion coefficient compared to that of ferromagnetic skyrmions. Consequently, our findings not only demonstrate the gyro-force dependence of the diffusion coefficient but also enable ultimately energy-efficient unconventional stochastic computing
Anisotropic Skyrmion Diffusion Controlled by Magnetic-Field-Induced Symmetry Breaking
Diffusion of particles has wide repercussions ranging from particle-based soft matter systems to solid state systems with particular electronic properties. Recently, in the field of magnetism, diffusion of magnetic skyrmions, topologically stabilized quasi-particles, has been demonstrated. Here we show that by applying a magnetic in-plane field and therefore breaking the symmetry of the system, the skyrmion diffusion becomes anisotropic with faster diffusion parallel to the field axis and slower diffusion perpendicular to it. We furthermore show that the absolute value of the applied field controls the absolute values of the diffusion coefficients so that one can thereby uniquely tune both the orientation of the diffusion and its strength. Based on the stochastic Thiele equation, we can explain the observed anisotropic diffusion as a result of the elliptical deformation of the skyrmions by the application of the in-plane field.publishe