Realization of macroscopic ratchet effect based on nonperiodic and uneven potentials

TL;DR

This paper demonstrates a macroscopic ratchet effect using hybrid nanostructures where superconducting vortices move in asymmetric potentials created by spin-ice nanomagnet arrays, showing consistent ratchet behavior across configurations.

Contribution

It introduces a novel ratchet device based on spin-ice nanostructures that produce asymmetric potentials for vortex motion, combining experimental observations with simulations.

Findings

Ratchet effect observed in various spin ice configurations

Vortices interact with uneven asymmetric potentials crossing charged Néel walls

The local ratchet effect results in a global macroscopic ratchet effect

Abstract

Ratchet devices allow turning an ac input signal into a dc output signal. A ratchet device is set by moving particles driven by zero averages forces on asymmetric potentials. Hybrid nanostructures combining artificially fabricated spin-ice nanomagnet arrays with superconducting films have been identified as a good choice to develop ratchet nanodevices. In our case, the asymmetric potentials are provided by charged N\'eel walls located in the vertices of the magnetic honeycomb array, whereas the role of moving particles is played by superconducting vortices. We have experimentally obtained ratchet effect for different spin ice I configurations and for vortex lattice moving parallel or perpendicular to the magnetic easy axes. Remarkably, the ratchet magnitudes are similar in all the experimental runs; i. e. different spin ice I configurations and in both relevant directions of the vortex lattice motion. We have simulated the interplay between vortex motion directions and a single asymmetric potential. It turns out vortices interact with uneven asymmetric potentials, when they move with trajectories crossing charged N\'eel walls with different orientations. Moreover, the appropriate asymmetric pair potentials which generate the local ratchet effect have been identified. In this rocking ratchet the particles (vortices) on the move are interacting each other (vortex lattice); therefore, the ratchet local effect turns into a global macroscopic effect. In summary, this ratchet device benefits from interacting particles moving in robust and topological protected type I spin ice landscapes.