Rocking ratchet induced by pure magnetic potentials with broken reflection symmetry

Abstract

A ratchet effect ͑the rectification of an ac injected current͒ 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 walls͒ 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 walls͒ 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.

Vortex ratchet reversal at fractional matching fields in kagomélike array with symmetric pinning centers

“…It is worth to mention that, in this kagomélike array, injecting an ac parallel to the Y axis ͑vortex motion parallel to the X axis͒ does not induce any dc output signal, in the same way that was already reported 2,26 for very different asymmetric potentials. Figure 5 shows the ratchet effect when the temperature is decreased, revealing experimental trends similar to Fig.…”

Realization of macroscopic ratchet effect based on nonperiodic and uneven potentials

“…The usual four-probe dc technique is used to record the data. We have to point out that we are dealing with adiabatic rocking ratchet, therefore the effect is independent of the frequency 23 . When the injected (ac) alternating (1 kHz frequency) input current is applied along one of the hard (easy) axes, the vortices move perpendicularly along one of the easy (hard) axes 8 .…”

Orbital magnetic ratchet effect

“…10,11 A ratchet effect purely magnetic in origin has been observed in a superconducting-magnetic nanostructure hybrid. 12 Pure spin current is generated in systems with non-uniform magnetic fields. 13 Possibility for large ratchet currents has been demonstrated in magnetic superlattices on the surface of topological insulators.…”