Rocking ratchet induced by pure magnetic potentials with broken reflection symmetry

TL;DR

This study demonstrates a purely magnetic ratchet effect in superconducting-magnetic hybrid nanostructures, where magnetic landscape asymmetry influences vortex motion, revealing a novel magnetic origin of rectification.

Contribution

It introduces a new magnetic ratchet mechanism based on remanent magnetic states in superconducting hybrids, distinct from structural ratchets.

Findings

Ratchet effect occurs only in ordered magnetic states with broken reflection symmetry.

Vortex motion perpendicular to magnetic domain walls induces rectification.

No ratchet effect in demagnetized or symmetric magnetic states.

Abstract

A ratchet effect (the rectification of an ac injected current) which is purely magnetic in origin has been observed in a superconducting-magnetic nanostructure hybrid. The hybrid consists of a superconducting Nb film in contact with an array of nanoscale magnetic triangles, circular rings or elliptical rings. The arrays were placed into well-defined remanent magnetic states by application of different magnetic field cycles. The stray fields from these remanent states provide a magnetic landscape which influences the motion of superconducting vortices. We examined both randomly varying landscapes from demagnetized samples, and ordered landscapes from samples at remanence after saturation in which the magnetic rings form parallel onion states containing two domain walls. The ratchet effect is absent if the rings are in the demagnetized state or if the vortices propagate parallel to the magnetic reflection symmetry axis (perpendicular to the magnetic domain walls) in the ordered onion state. On the other hand, when the vortices move perpendicular to the magnetic reflection symmetry axis in the ordered onion state (parallel to the domain walls) a clear ratchet effect is observed. This behavior differs qualitatively from that observed in samples containing arrays of triangular Ni nanostructures, which show a ratchet of structural origin.