Use of two-photon lithography with a negative resist and processing to realise cylindrical magnetic nanowires

Cylindrical magnetic nanowires have been shown to exhibit a vast array of fascinating 10 spin textures, including chiral domains, skyrmion tubes and topologically protected domain walls 11 that harbor Bloch points. Here we present a novel methodology that utilizes two-photon 12 lithography in order to realize tailored 3D porous templates upon prefabricated electrodes. 13 Electrochemical deposition is used to fill these porous templates, and reactive ion etching is used to 14 free the encased magnetic nanowires. The nanowires are found to have a diameter of 420nm, length 15 of 2.82m and surface roughness of 7.6nm. Magnetic force microscopy in an externally applied field 16 suggests a complex spiraling magnetization state, which demagnetizes via the production of 17 vortices of alternating chirality. Detailed micro-magnetic simulations confirm such a state and a 18 qualitative agreement is found with respect to the switching of experimental nanowires. 19 Surprisingly, simulations also indicate the presence of a Bloch point as a metastable state during the 20 switching process. Our work provides a new means to realize 3D magnetic nanowires of controlled 21 geometry and calculations suggest a further reduction in diameter to sub-200nm will be possible, 22 providing access to a regime of ultrafast domain wall motion

In-situ fabricated 3D micro-lenses for photonic integrated circuits

Aspheric astigmatic polymer micro-lenses were fabricated directly onto photonic integrated circuits using two-photon lithography. We observed a 12.6 dB improvement in the free space coupling efficiency between integrated ridge laser pairs with micro-lenses to those without

Asymmetric dual Bloch point domain walls in cylindrical magnetic nanowires

Cylindrical magnetic nanowires have been studied extensively over the past ten years due to the presence of domain walls with novel topology and outstanding dynamic properties. In soft magnetic systems, where shape anisotropy forces the magnetization along the wire axis, and for radii above 50 nm, two topologically distinct walls have been previously identified. The Bloch point wall (BPW) has a circulating magnetization texture around the circumference and contains a single Bloch point within the center of the wire cross section. In contrast, asymmetric transverse walls (ATWs) have a circulating magnetization structure on the surface and contain two topological defects, a vortex and an antivortex on opposing sides. These surface defects are connected via a vortex tube that penetrates the volume. In this study, we have numerically investigated the domain wall magnetization textures for nickel nanowires of radii 50–120 nm. Beyond reproducing the known BPW and ATW topology, we discover a new domain wall type that contains aspects of both. This new domain wall type, which we call asymmetric dual Bloch point wall (ADBPW), has surface vortices similar to an ATW and two Bloch-point textures adjacent to the internal vortex tube. Time-resolved simulations investigating the stability of ADBPW show its field-driven transformation into a BPW via the ejection of a single Bloch point at the surface and subsequent annihilation of surface vortices

A magnetic map leads juvenile European eels to the Gulf Stream

Migration allows animals to track the environmental conditions that maximize growth, survival, and reproduction [ 1–3 ]. Improved understanding of the mechanisms underlying migrations allows for improved management of species and ecosystems [ 1–4 ]. For centuries, the catadromous European eel (Anguilla anguilla) has provided one of Europe’s most important fisheries and has sparked considerable scientific inquiry, most recently owing to the dramatic collapse of juvenile recruitment [ 5 ]. Larval eels are transported by ocean currents associated with the Gulf Stream System from Sargasso Sea breeding grounds to coastal and freshwater habitats from North Africa to Scandinavia [ 6, 7 ]. After a decade or more, maturing adults migrate back to the Sargasso Sea, spawn, and die [ 8 ]. However, the migratory mechanisms that bring juvenile eels to Europe and return adults to the Sargasso Sea remain equivocal [ 9, 10 ]. Here, we used a “magnetic displacement” experiment [ 11, 12 ] to show that the orientation of juvenile eels varies in response to subtle differences in magnetic field intensity and inclination angle along their marine migration route. Simulations using an ocean circulation model revealed that even weakly swimming in the experimentally observed directions at the locations corresponding to the magnetic displacements would increase entrainment of juvenile eels into the Gulf Stream System. These findings provide new insight into the migration ecology and recruitment dynamics of eels and suggest that an adaptive magnetic map, tuned to large-scale features of ocean circulation, facilitates the vast oceanic migrations of the Anguilla genu

Magnetic Charge Propagation upon a 3D Artificial Spin-ice

Magnetic charge propagation in bulk frustrated materials has yielded a paradigm-shift in science, allowing the symmetry between electricity and magnetism to be studied. Recent work is now suggesting magnetic charge dynamics upon the spin-ice surface may have important implications in determining the ordering and associated phase space. Here we detail a 3D artificial spin-ice, a 3D nanostructured array of magnetic islands which captures the exact geometry of bulk systems, allowing field-driven dynamics of magnetic charge to be directly visualized upon the surface. Using magnetic microscopy, we observe vastly different magnetic charge dynamics along two principle directions. These striking differences are found to be due to the surface-termination and associated coordination which yields different energetics and interaction strengths for magnetic charges upon the surface

Direct observation and control of magnetic monopole defects in an artificial spin-ice material

Magnetic monopoles have stimulated a great amount of theoretical and experimental interest since their prediction by Dirac in 1931. To date, their presence has evaded detection in high energy experiments despite intensive efforts. Recently, entities that mimic magnetic monopoles have been observed in bulk and planar frustrated materials known as spin-ice materials, and artificial spin-ice materials, respectively. In this paper we discuss the formation of these so-called monopole defects within a cobalt honeycomb artificial spin-ice lattice. Experimental results and micromagnetic simulations show that monopole defects of opposite sign are created at the boundaries of the lattice, and move in opposing directions. Discrepancies between simulations and experimental results demonstrate the importance of quenched disorder. Furthermore, we show that controlled edge nucleated monopole defect formation can be realized with the use of soft magnetic injection pads, which is a very promising development for technological applications based upon magnetic charge

Combining two-photon lithography with laser ablation of sacrificial layers: a route to isolated 3D magnetic nanostructures

Three-dimensional (3D) nanostructured functional materials are important systems allowing new means for intricate control of electromagnetic properties. A key problem is realising a 3D printing methodology on the nanoscale that can yield a range of functional materials. In this article, it is shown that two-photon lithography, when combined with laser ablation of sacrificial layers, can be used to realise such a vision and produce 3D functional nanomaterials of complex geometry. Proof-of-principle is first shown by fabricating planar magnetic nanowires raised above the substrate that exhibit controlled domain wall injection and propagation. Secondly, 3D artificial spin-ice (3DASI) structures are fabricated, whose complex switching can be probed using optical magnetometry. We show that by careful analysis of the magneto-optical Kerr effect signal and by comparison with micromagnetic simulations, depth dependent switching information can be obtained from the 3DASI lattice. The work paves the way for new materials, which exploit additional physics provided by non-trivial 3D geometries

Realisation of a frustrated 3D magnetic nanowire lattice

Patterning nanomagnets in three-dimensions presents a new paradigm in condensed matter physics and allows access to a plethora of fundamental phenomena including robust spin textures, magnetic metamaterials that are home to defects carrying magnetic charge and ultrahigh density devices that store information in three dimensions. However, the nanostructuring of functional magnetic materials into complex three-dimensional geometries has thus far proven to be a formidable challenge. Here we show magnetic nanowires can be arranged into 3D frustrated magnetic nanowire lattices by using a combination of 3D polymer nanoprinting and metallic deposition. The fabricated nanowires are single domain and they switch via nucleation and propagation of domain walls. Deep nanoscale magnetic imaging and finite element simulations elucidate the spin texture present on the 3D nanostructured lattice. Our study demonstrates a generic platform for the production of 3D nanostructured magnetic materials allowing the realisation of racetrack memory devices and 3D nanostructured systems that mimic bulk frustrated crystals