Travelling wave ratchets allow us to control the drift and diffusion of magnetic nanoparticles across a series of Bloch walls.
News from Nov 28, 2018
The performance of small-scale devices is often limited by the presence of thermal fluctuations, whereas in micro- and nanofluidic applications the fluctuations may be used to spread reactants or drugs. In this combined experimental and theoretical study, we demonstrate the controlled net motion and the enhancement of diffusion of magnetic nanoparticles driven above a garnet film across a series of Bloch walls. We use a rotating magnetic field to break the symmetry and generate a traveling wave potential. To rationalize the experiment, we develop an analytically tractable model that offers insights into the transport characteristics and enables their frequency tuning. The predictions of the theory and more accurate numerical simulations are in good agreement with the experimental data. Our technique to control thermal fluctuations of driven magnetic nanoparticles represents a versatile and powerful way to programmably transport magnetic colloidal matter in a fluid, opening the doors to different fluidic applications based on exploiting magnetic domain wall ratchets.
Enhancing nanoparticle diffusion on a unidirectional domain wall magnetic ratchet,
R. Stoop, A. V. Straube, and P. Tierno, Nano Lett. 19, 433 (2019)