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Antiskyrmions, in which the magnetization rotates both as a transverse helix and as a cycloid, are found in acentric tetragonal Heusler compounds over a wide range of temperatures. Magnetic appeal of antiskyrmions Skyrmions, topologically stable, vortex-like spin textures, are of great interest for the development of a new generation of magnetic devices, in which they could carry or store information while remaining robust against disturbances. So far, only two types of skyrmion have been observed experimentally, the Bloch skyrmion and the Néel skyrmion, but Stuart Parkin and colleagues have now observed another type to join the family: the antiskyrmion. These are observed in a type of magnetic material called a centric tetragonal Heusler compound, which has unusual crystal symmetry. An antiskyrmion lattice state appears when magnetic fields are applied along the tetragonal axis, over a wide temperature interval. Because antiskyrmions break the cylindrical symmetry and carry a quadrupolar moment, their properties may differ from those of Bloch and Néel skyrmions and so they offer new opportunities for control. Magnetic skyrmions are topologically stable, vortex-like objects surrounded by chiral boundaries that separate a region of reversed magnetization from the surrounding magnetized material 1 , 2 , 3 . They are closely related to nanoscopic chiral magnetic domain walls, which could be used as memory and logic elements for conventional and neuromorphic computing applications that go beyond Moore’s law. Of particular interest is ‘racetrack memory’, which is composed of vertical magnetic nanowires, each accommodating of the order of 100 domain walls, and that shows promise as a solid state, non-volatile memory with exceptional capacity and performance 4 , 5 . Its performance is derived from the very high speeds (up to one kilometre per second) at which chiral domain walls can be moved with nanosecond current pulses in synthetic antiferromagnet racetracks. Because skyrmions are essentially composed of a pair of chiral domain walls closed in on themselves, but are, in principle, more stable to perturbations than the component domain walls themselves, they are attractive for use in spintronic applications, notably racetrack memory. Stabilization of skyrmions has generally been achieved in systems with broken inversion symmetry, in which the asymmetric Dzyaloshinskii–Moriya interaction modifies the uniform magnetic state to a swirling state 6 , 7 . Depending on the crystal symmetry, two distinct types of skyrmions have been observed experimentally, namely, Bloch 7 , 8 and Néel skyrmions 9 . Here we present the experimental manifestation of another type of skyrmion—the magnetic antiskyrmion—in acentric tetragonal Heusler compounds with D 2d crystal symmetry. Antiskyrmions are characterized by boundary walls that have alternating Bloch and Néel type as one traces around the boundary. A spiral magnetic ground-state, which propagates in the tetragonal basal plane, is transformed into an antiskyrmion lattice state under magnetic fields applied along the tetragonal axis over a wide range of temperatures. Direct imaging by Lorentz transmission electron microscopy shows field-stabilized antiskyrmion lattices and isolated antiskyrmions from 100 kelvin to well beyond room temperature, and zero-field metastable antiskyrmions at low temperatures. These results enlarge the family of magnetic skyrmions and pave the way to the engineering of complex bespoke designed skyrmionic structures.

The fabrication of three-dimensional nanostructures is key to the development of next-generation nanoelectronic devices with a low device footprint. Magnetic racetrack memory encodes data in a series of magnetic domain walls that are moved by current pulses along magnetic nanowires. To date, most studies have focused on two-dimensional racetracks. Here we introduce a lift-off and transfer method to fabricate three-dimensional racetracks from freestanding magnetic heterostructures grown on a water-soluble sacrificial release layer. First, we create two-dimensional racetracks from freestanding films transferred onto sapphire substrates and show that they have nearly identical characteristics compared with the films before transfer. Second, we design three-dimensional racetracks by covering protrusions patterned on a sapphire wafer with freestanding magnetic heterostructures. We demonstrate current-induced domain-wall motion for synthetic antiferromagnetic three-dimensional racetracks with protrusions of up to 900 nm in height. Freestanding magnetic layers, as demonstrated here, may enable future spintronic devices with high packing density and low energy consumption.A lift-off and transfer method enables the fabrication of efficient three-dimensional racetrack memory devices fabricated from freestanding magnetic heterostructures on a prepatterned substrate and may—in the future—allow for advanced three-dimensional nanostructures in next-generation nanoelectronic devices with a low device footprint.

Based on the extended Landau–Lifshitz–Gilbert method, the properties of current driven domain wall movement in U-shaped magnetic nanowires and the effect of spin wave assistance on their properties have been investigated. The results show that changes of the curvature radius of magnetic nanowire can cause the additional pinning action and the pinning action will weaken the speed of current driven domain wall movement. For U-shaped magnetic nanowires, the changes of curvature radius can be represented by the radius R at the bend. The results show that the decline of its speed non-monotonically increases with the decrease of the bending radius of magnetic nanowires. On the other hand, the assistance of applying spin waves not only enhances the movement of magnetic domain walls but also weakens the pinning action. Further research has shown that applying the appropriate spin waves at the bend changing point can completely eliminate the influence induced by bend changing, in order to ensure uniform and stable movement of current driven magnetic domain walls in U-shaped magnetic nanowires, and achieve the current driven three-dimensional racetrack memory technology.

Only 60-75% of conventional kidney stone surgeries achieve complete stone-free status. Up to 30% of patients with residual fragments <2 mm in size experience subsequent stone-related complications. Here we demonstrate a stone retrieval technology in which fragments are rendered magnetizable with a magnetic hydrogel so that they can be easily retrieved with a simple magnetic tool. The magnetic hydrogel facilitates robust in vitro capture of stone fragments of clinically relevant sizes and compositions. The hydrogel components exhibit no cytotoxicity in cell culture and only superficial effects on ex vivo human urothelium and in vivo mouse bladders. Furthermore, the hydrogel demonstrates antimicrobial activity against common uropathogens on par with that of common antibiotics. By enabling the efficient retrieval of kidney stone fragments, our method can lead to improved stone-free rates and patient outcomes. The success of surgical kidney stone removal is limited by the ability to efficiently retrieve stone fragments, resulting in incomplete stone clearance and subsequent morbidity. Here, the authors show the efficacy and biocompatibility of a magnetic hydrogel that selectively coats human kidney stone fragments in vitro allowing their total extraction using a magnetic wire.

Topological defects, or singularities, play a key role in the statics and dynamics of complex systems. In magnetism, Bloch point singularities represent point defects that mediate the nucleation of textures such as skyrmions and hopfions. While these textures are typically stabilised in chiral magnets, the influence of chirality and symmetry breaking on Bloch point singularities remains relatively unexplored. Here, we harness advanced three-dimensional nanofabrication to explore the influence of symmetry breaking on Bloch point textures by introducing controlled nano-curvature in a ferromagnetic nanowire. Combining X-ray magnetic microscopy with the application of in situ magnetic fields, we demonstrate that Bloch point singularity-containing domain walls are stabilised in straight regions of the sample, and determine that curvature can be used to tune the energy landscape of the Bloch points. Not only are we able to pattern pinning points but, by controlling the gradient of curvature, we define asymmetric potential wells to realise a robust Bloch point texture shift-register with non-reciprocal behaviour. These insights into the influence of symmetry on singularities offer a route to the controlled nucleation and propagation of topological textures, providing opportunities for logic and computing devices. Three-dimensional nanofabrication allows for the precise tailoring of curvature of magnetic nanowires, and therefore the local symmetry breaking. Here, Ruiz-Gomez et al use this control to study the interaction of domain walls with local curvature, engineering potential wells and shift registers.

The detection of magnetic nanoparticles in a liquid medium and the quantification of their concentration have the potential to improve the efficiency of several relevant applications in different fields, including medicine, environmental remediation, and mechanical engineering. To this end, sensors based on the magneto-impedance effect have attracted much attention due to their high sensitivity to the stray magnetic field generated by magnetic nanoparticles, their simple fabrication process, and their relatively low cost. To improve the sensitivity of these sensors, a multidisciplinary approach is required to study a wide range of soft magnetic materials as sensing elements and to customize the magnetic properties of nanoparticles. The combination of magneto-impedance sensors with ad hoc microfluidic systems favors the design of integrated portable devices with high specificity towards magnetic ferrofluids, allowing the use of very small sample volumes and making measurements faster and more reliable. In this work, a magneto-impedance sensor based on an amorphous Fe73.5Nb3Cu1Si13.5B9 wire as the sensing element is integrated into a customized millifluidic chip. The sensor detects the presence of magnetic nanoparticles in the ferrofluid and distinguishes the different stray fields generated by single-domain superparamagnetic iron oxide nanoparticles or magnetically blocked Co-ferrite nanoparticles.

The magnetic characteristics of FINEMET type glass-coated nanowires and submicron wires are investigated by taking into account the structural evolution induced by specific annealing all the way from a fully amorphous state to a nanocrystalline structure. The differences between the magnetic properties of these ultrathin wires and those of the thicker glass-coated microwires and “conventional” wires with similar structures have been emphasized and explained phenomenologically. The domain wall propagation in these novel nanowires and submicron wires, featuring a combination between an amorphous and a crystalline structure, has also been studied, given the recent interest in the preparation and investigation of new materials suitable for the development of domain wall logic applications.

A novel approach for a non-volatile destructive readout memory application using bistable magnetic nanowire arrays is presented. The encoded information is stored as binary 1 and 0 by groups of NWs magnetized in the positive and negative states, respectively. We leverage the naturally occurring switching field distribution of the NW array and a tailored alternating decreasing magnetic field to program remanent magnetic states. To retrieve the information, the measured remagnetization curve exhibits a star-like behavior with jumps and plateaus and its derivative converts this information to a binary-type format. Two encoding and readout schemes are proposed and validated: binary bits and barcodes. For each case, the implementation and optimization procedures are illustrated, along with the required processing to obtain a useful readout signal. This strategy holds potential for non-volatile memory applications in which the stored information is erased during reading and can be reused indefinitely. Graphical abstract

The interfusion of impurities such as metallic wear debris has been a major issue in the manufacturing process of foods, medicines and industrial products. Such debris originates with wearing of stainless-steel pipe joints or mechanical moving parts. Since the debris shows ferromagnetic properties by undergoing the strain-induced martensitic transformation of non-magnetic SUS304 (X5CrNi18-10), the magnetic separation system is much efficient to remove such debris from raw materials. In order to study the magnetic separation properties for the martensitic transformation fine particles, the several kinds of magnetic powder with different magnetization were prepared by controlling the amount of martensitic transformation by heat-treating SUS304 powders. The magnetic separation performance was evaluated by the high gradient magnetic separation (HGMS) experiments using the multilayer unidirectional magnetic wire filter under dry condition. The experimental results and FEM particle trajectory simulations revealed that the SUS304 powders transformed into martensite were removed at high speed of 0.1 m/s by the superconducting HGMS in a relatively low magnetic field.

Orthogonal fluxgates in fundamental mode based on (Co0.94Fe0.06)72.5Si12.5B15 cores have recorded very low noise in literature, especially if Joule annealing is performed on the core for a short period of time. However, for annealing time longer than 20–30 min, the noise of the sensor has a tendency to increase. In this work, we investigated this phenomenon, and we have found its origin in a monotonic increase of magnetostriction during the annealing process. We show that the wires with vanishing magnetostriction in their as-cast form exhibit positive magnetostriction after long-time annealing (more than 30 min), which increases the noise of the sensor. After researching the effect of the magnetostriction after annealing on the noise, we propose an alloy with a reduced amount of iron. Less iron leads to a larger as-cast negative magnetostriction, which becomes almost zero after long-time annealing (60 min), bringing further reduction of noise. We prove this effect on two wires from two different manufacturers, although with the same composition. The noise decrease with prolonged annealing is mainly observable in the low-frequency region: at 100 mHz, the noise of a single-wire sensor decreased from 20pT/Hz to 6pT/Hz when the annealing time was prolonged from 10 to 60 min.