Nonvolatile logic networks based on spintronic and nanomagnetic technologies have the potential to create high‐speed, ultralow power computational architectures. This article explores the feasibility of “chirality‐encoded domain wall logic,” a nanomagnetic logic architecture where data are encoded by the chiral structures of mobile domain walls in networks of ferromagnetic nanowires and processed by the chiral structures' interactions with geometric features of the networks. High‐resolution magnetic imaging is used to test two critical functionalities: the inversion of domain wall chirality at tailored artificial defect sites (logical NOT gates) and the chirality‐selective output of domain walls from 2‐in‐1‐out nanowire junctions (common operation to AND/NAND/OR/NOR gates). The measurements demonstrate both operations can be performed to a good degree of fidelity even in the presence of complex magnetization dynamics that would normally be expected to destroy chirality‐encoded information. Together, these results represent a strong indication of the feasibility of devices where chiral magnetization textures are used to directly carry, rather than merely delineate, data.

Emergent behaviors occur when simple interactions between a system's constituent elements produce properties that the individual elements do not exhibit in isolation. This article reports tunable emergent behaviors observed in domain wall (DW) populations of arrays of interconnected magnetic ring‐shaped nanowires under an applied rotating magnetic field. DWs interact stochastically at ring junctions to create mechanisms of DW population loss and gain. These combine to give a dynamic, field‐dependent equilibrium DW population that is a robust and emergent property of the array, despite highly varied local magnetic configurations. The magnetic ring arrays’ properties (e.g., non‐linear behavior, “fading memory” to changes in field, fabrication repeatability, and scalability) suggest they are an interesting candidate system for realizing reservoir computing (RC), a form of neuromorphic computing, in hardware. By way of example, simulations of ring arrays performing RC approaches 100% success in classifying spoken digits for single speakers.

We explore the feasibility of exciting localized spin wave modes in ferromagnetic nanostructures using surface acoustic waves. Time-resolved Faraday effect is used to probe the magnetization dynamics of an array of nickel nanowires. The optical pump pulse excites both spin wave modes of the nanowires, and acoustic modes of the substrate, and we observe that when the frequencies of these coincide the amplitude of magnetization dynamics are substantially enhanced due magnetoelastic coupling between the two. Notably, by tuning the magnitude of an externally applied magnetic field, optically excited surface acoustic waves can selectively excite either the upper or lower branches of a splitting in the nanowire's spin wave spectrum, which micromagnetic simulations indicate to be caused by localization of spin waves in different parts of the nanowire. Thus, our results indicate the feasibility of using acoustic waves to selectively excite spatially confined spin waves, an approach that may find utility in future magnonic devices where coherent structural deformations could be used as coherent sources of propagating spin waves.

The interactions of vortex domain walls with corners in planar magnetic nanowires are probed using magnetic soft X-ray transmission microscopy. We show that when the domain walls are propagated into sharp corners using applied magnetic fields above a critical value, their chiralities are rectified to either clockwise or anticlockwise circulation depending on whether the corners turn left or right. Single-shot focused magneto-optic Kerr effect measurements are then used to demonstrate how, when combined with modes of domain propagation that conserve vortex chirality, this allows us to dramatically reduce the stochasticity of domain pinning at artificial defect sites. Our results provide a tool for controlling domain wall chirality and pinning behavior both in further experimental studies and in future domain wall-based memory, logic and sensor technologies. Devices based on the motion of domain walls (DWs) in magnetic nanowires have been in development for over a decade. [1][2][3] While simple descriptions visualize DWs as rigid particles, DWs actually have complex internal magnetization structures 4 that change dynamically as they propagate. [5][6][7] Key to understanding DW structure is the concept of chirality, which describes the sense of magnetization rotation across the DW. For example, in the case of vortex DWs (VDWs), chirality dictates whether their internal magnetization rotates clockwise (CW) or anticlockwise (ACW) around a central out-of-plane core.Chirality has a strong influence on DW behavior: VDWs with opposite chiralities pin differently at notches, resulting in stochastic depinning field distributions in systems where chirality is ill-defined. 8,9 Furthermore, chirality dictates the paths of DWs in branched nanowires, and therefore the geometry of Dirac strings in artificial spin-ice lattices. 10 In systems where DW structure can be stabilized, chirality also offers a binary degree of freedom, leading to proposals for chirality-based logic networks. 11 DWs injected using injection pads or current lines have random chiralities, leading to uncontrolled pinning behaviors. However, by breaking the symmetry of these features, chirality can be controlled at the point of injection. 10,12 Controlling and manipulating chiralities during propagation is more challenging, but can be achieved by interacting DWs with orthogonal nanowire sections, 13 large notches, 14 or enddomains; 15 however, these approaches all involve the introduction of large defects into the nanowires. Pulsed rotating fields can be used to select DW chirality in ring-shaped nanowires, 16 but this approach would be complex to implement in devices.In this paper, we propose a simple method of controlling DW chirality in continuous nanowires. We show that DWs propagated ballistically into sharp nanowire corners are reliably rectified to either CW or ACW chirality depending on whether the corner turns left or right. We then demonstrate how this approach can be exploited to dramatically reduce the stochasticity of pinning at artificial defect...

Despite the high incidence of tendon injuries worldwide, an optimal treatment strategy has yet to be defined. A key challenge for tendon repair is the alignment of the repaired matrix into orientations which provide maximal mechanical strength. Using oriented implants for tissue growth combined with either exogenous or endogenous stem cells may provide a solution. Previous research has shown how oriented fiber-like structures within 3D scaffolds can provide a framework for organized extracellular matrix deposition. In this article, we present our data on the remote magnetic alignment of collagen hydrogels which facilitates long-term collagen orientation. Magnetic nanoparticles (MNPs) at varying concentrations can be contained within collagen hydrogels. Our data show how, in response to the magnetic field lines, MNPs align and form string-like structures orientating at 90 degrees from the applied magnetic field from our device. This can be visualized by light and fluorescence microscopy, and it persists for 21 days post-application of the magnetic field. Confocal microscopy demonstrates the anisotropic macroscale structure of MNP-laden collagen gels subjected to a magnetic field, compared to gels without MNP dosing. Matrix fibrillation was compared between non- and biofunctionalized MNP hydrogels, and different gels dosed with varying MNP concentrations. Human adipose stem cells (hASCs) seeded within the magnetically aligned gels were observed to align in parallel to MNP and collagen orientation 7 days post-application of the magnetic field. hASCs seeded in isotropic gels were randomly organized. Tenocyte-likeness of the cells 7 days post-seeding in collagen I scaffolds was confirmed by the positive expression of tenomodulin and scleraxis proteins. To summarize, we have developed a convenient, non-invasive protocol to control the collagen I hydrogel architecture. Through the presence or absence of MNP dosing and a magnetic field, collagen can be remotely aligned or randomly organized, respectively, in situ. Tendon-like cells were observed to organize in parallel to unidirectionally aligned collagen fibers and polydirectionally in non-aligned collagen constructs. In this way, we were able to engineer the constructs emulating a physiologically and pathologically relevant tendon niche. This can be considered as an innovative approach particularly useful in tissue engineering or organ-on-a-chip applications for remotely controlling collagen matrix organization to recapitulate the native tendon.