Fig. 1: Transport mechanism and magnetic landscapes.
From: Emergent colloidal currents across ordered and disordered landscapes
a Illustration of paramagnetic colloids driven above a ferrite garnet film (FGF), with small arrows indicating the magnetization direction of the bubbles. One unit cell is shown in red with the 12 crystallographic directions, with lattice constant a = 3 μm. The rotating magnetic field is indicated by the arrow in the green circle with the dashed arrows indicating the sense of rotation; the particles move along the direction of the green arrow. b, c Polarization microscope images of a portion of the FGF with (b ordered (η6 = 0.05) and c disordered (η6 = 0.45) magnetic bubbles; the scale bar is 20 μm. Colloidal particles appear as dark circles. d Radial distribution g(r) and e g6(r) for the ordered (blue) and disordered (red) lattices, calculated from a total area of 151 × 113 μm2. The inset in g(r) illustrates the difference in absolute value between the two g(r). f Energy landscape of the magnetic lattice (z = 0.4 a) at different times from left to right; scale bar is a/2. Energy minima (dark blue) and maxima (yellow) correspond to (−2000 kBT) and (−240 kBT), respectively. The particle moves to the right, the red arrow indicates the direction of motion. g Normalized single-particle speed \({\bar{v}}_{x}^{{{{{{{{\rm{s}}}}}}}}}\) versus angular frequency ω from experiments (scattered data) for ordered case, η6 = 0.05, and disordered one, η6 = 0.45; η6 denotes the exponent of the bond correlation function g6(r). Continuous lines are fits to the synchronous and asynchronous regimes and yield a critical frequency of ωc = 37.3 rad s−1. The down-pointing arrow indicates the location of ωc = 50.3 rad s−1. The experimental data are averaged over different independent measurements, and the error bars (inside the orange circles) indicate the standard error, error bars in the squares are smaller than the symbols.
