Topologically protected superconducting ratchet effect generated by spin-ice nanomagnets

Abstract

We have designed, fabricated and tested a robust superconducting ratchet device based on topologically frustrated spin-ice nanomagnets. The device is made of a magnetic Co honeycomb array embedded in a superconducting Nb film. This device is based on three simple mechanisms: i) the topology of the Co honeycomb array frustrates in-plane magnetic configurations in the array yielding a distribution of magnetic charges which can be ordered or disordered with in-plane magnetic fields, following spin-ice rules; ii) the local vertex magnetization, which consists of a magnetic half vortex with two charged magnetic Néel walls; iii) the interaction between superconducting vortices and the asymmetric potentials provided by the Néel walls. The combination of these elements leads to a superconducting ratchet effect. Thus, superconducting vortices driven by alternating forces and moving on magnetic half vortices generate a unidirectional net vortex flow. This ratchet effect is independent of the distribution of magnetic charges in the array.

Reconfigurable Pinwheel Artificial-Spin-Ice and Superconductor Hybrid Device

“…The controlled magnetization of magnetic nanostructures with an applied magnetic field allows in-situ tuning of the vortex pinning potential, enabling reconfigurable superconducting functionalities [25][26][27] . Recently, a particular type of magnetic nanostructure, called artificial spin ice (ASI), was used as nanoscale reconfigurable magnetic landscapes to modulate the behavior of vortices in a hybrid ferromagnetic/superconducting structure 28,29 . The highly tunable and wide spectrum of magnetic configurations of artificial spin ice structures allow the tuning of vortex motion and superconducting transport properties in a more flexible way.…”

“…The highly tunable and wide spectrum of magnetic configurations of artificial spin ice structures allow the tuning of vortex motion and superconducting transport properties in a more flexible way. For example, a reprogrammable vortex diode has been recently realized by patterning a tri-axial artificial spin ice on top of a superconducting film 28 , and a reversible vortex ratchet effect was demonstrated by using an artificial kagome spin ice 29 . Here, we present a new artificial-spin-ice and superconductor heterostructure consisting of a pinwheel (or chiral) ASI array on top of a superconducting film ( Figure 1a).…”

“…The pinwheel ASI forms a four-fold degenerate ferromagnetic order with easily tunable magnetic configurations via an in-plane external magnetic field 33 . The interaction between a nanomagnet in an ASI and a vortex in a superconductor can be viewed as a dumbbell of magnetic charges 'one negative, one positive' attracting and/or repelling a superconducting vortex, respectively 28 . As shown in Figure 1a, one unique feature of pinwheel ASI is the formation of alternating rows of positive and negative magnetic charge chains, creating alternating negative (low) potential valleys and positive (high) potential ridges for superconducting vortices.…”

Advances in artificial spin ice

“…Alternatively, complex anisotropies can be introduced with single-crystal materials 24,168 , which can also be adapted by modifying the nanomagnet shape 169 . Interesting behaviour can be obtained with hybrid thinfilm systems combining, for example, different magnetic thin films, artificial spin ices with superconductors 170,171 or magnetostrictive and piezoelectric materials in so-called multiferroic composites 3 .…”

Current-controlled nanomagnetic writing for reconfigurable magnonic crystals

“…ersatile, low-power means to selectively control magnetization states at the nanoscale are critical across a host of applications, both in fundamental science and deviceoriented systems. Alongside mature technologies such as data storage, nanomagnetic arrays support a host of more recent applications including neuromorphic computation [1][2][3][4][5] , superconducting vortex control [6][7][8][9] and reconfigurable magnonic crystals [10][11][12][13][14]. RMCs are nanopatterned metamaterials harnessing varying magnetic configurations to manipulate and store information by tuning magnonic (spin-wave) dynamics [15][16][17][18][19][20][21][22][23][24][25][26] .…”