This study compares the propulsion of scaled-up helical microrobot models, based on hard- and soft-magnetic elements under rotating magnetic fields. The experiments were performed at the millimeter scale and interpreted using hydrodynamic scaling laws to predict microscale behavior. Results show that hard-magnetic microrobots achieved step-out frequencies and maximum propulsion speeds 4.5 times higher than soft-magnetic microrobots. Below saturation magnetization, soft-magnetic microrobots demonstrated similar performance irrespective of magnetic susceptibility, highlighting that torque generation in these materials is purely geometry-dependent. Employing a tapered ribbon design increased propulsion speed by a factor of 3.5 compared to regular helical designs. These results show that the impact of using soft rather than hard magnets is manageable, allowing for biodegradable magnets such as pure iron. The theory and experiments in this paper provide a quantitative basis for selecting materials and designs.

Thin-film giant magnetoimpedance (GMI) structures are promising candidates for high-frequency magnetic sensing, with their performance governed by the interplay of electronic transport, magnetic softness, and ferromagnetic resonance (FMR). Optimisation therefore requires a comprehensive understanding of the properties of soft magnetic materials. This study investigates the structural, electric, magnetic, and GMI properties of sputtered amorphous CoNbZr single layers, amorphous CoNbZr/Au multilayers, and crystalline NiFe/Au multilayers. GMI measurements reveal distinct FMR frequencies of 1.4 GHz (CoNbZr), 0.7 GHz (CoNbZr/Au), and 0.5 GHz (NiFe/Au). Introducing Au interlayers into CoNbZr lowers the FMR frequency by 50% and enhances the maximum GMI ratio by a comparable margin relative to the single-layer film. At 1.8 GHz, the highest GMI performance is observed in a 20μm×5000μm CoNbZr/Au strip, yielding 300% with a sensitivity of 249%/kAm⁻¹. Under identical conditions, single-layer CoNbZr reaches 180% (169%/kAm⁻¹) and NiFe/Au 280% (183%/kAm⁻¹), confirming the superior response of the CoNbZr/Au multilayer. These improvements are attributed to differences in in-plane demagnetising factors and saturation magnetisations, providing design guidelines for the development of resonant GHz-range GMI sensors.

Peripheral Nerve Injury (PNI) leads to significant motor and sensory impairments, with limited recovery potential in injuries exceeding 3 cm, Conventional treatments often fail to achieve full functional restoration. Suction-based approaches at lesion sites have demonstrated promising outcomes in nerve regeneration. This work presents a novel wireless, magnetically actuated micropump composed of biodegradable materials, such as poly(octamethylene-maleate(anhydride)citrate) (POMaC), for nerve repair applications. The micropump integrates a magnetic ring within its membrane, enabling deflection under alternating magnetic field (4Hz,pm 150mT), generating a net under-pressure of 1.3 kPa within 8 minutes. It provides a potential solution to facilitate nerve healing.

Creation and manipulation of magnetic domain walls (DWs) are a core subject of research in developing prototype devices for spintronic applications. DWs can be created artificially and moved by applying either a magnetic field or an electric current, as has been extensively investigated. Here, we study the DW pinning and depinning in half-metallic ferromagnetic La_0.7Sr_0.3MnO₃ nanostructures with a notch that is about 90% of the width of the wire. By measuring the magnetoresistance of the notched wires while sweeping the magnetic field, we unambiguously observe DW pinning and depinning from 10 to 300 K. Analysis of the temperature dependence reveals that both ΔR (the DW resistance) and ΔR/R₀ (R₀ is the resistance at zero field) are proportional to the temperature. The DW resistivity is calculated to be of the order of 10⁻¹⁷Ωm² at 10 K and 10⁻¹⁵Ωm² at 300 K. The latter value agrees with the reported intrinsic DW resistivity in films. In addition, we find approximately constant ΔR and ΔR/R₀ for widths from 1.8µm and a pronounced increase in both quantities when the width goes down to 755 nm. With the extracted magnetocrystalline anisotropy parameters from the measurements of the remanent magnetization and the magnetic torque as function of angle of the magnetic field with respect to the substrate normal, we further perform micromagnetic simulations and obtain results consistent with the experimental data. Our work may promote designing relevant prototypes and may constitute a platform to explore the effect of spin torque transfer on DWs.

Amorphous sputtered Co-based thin films are widely used as soft magnetic materials in applications such as sensors, inductors and magnetic flux concentrators. The magnetic properties of these films can be controlled by deposition parameters like film thickness, argon pressure, deposition rate and others. In this study, we present a detailed investigation of the magnetic properties of RF-sputtered Co₉₀Nb₈Zr₂ films with thicknesses ranging from 52 nm to 1040 nm. These amorphous films exhibit an average saturation magnetisation of (1.01 ± 0.04) MA/m. As the film thickness increases, there is a significant decrease in coercivity, remanent-to-saturation magnetisation ratio M_r/M_s, and maximum permeability. The change in macroscopic magnetic properties is also reflected by the domain structure. At a thickness of 52 nm, the remanent domain state shows irregular domains, while films thicknesses above 208 nm exhibit flux-closure domain structures instead. The thickness-dependent modifications are attributed to the transition between Néel and Bloch type domain walls, which is expected to occur at approximately 84 nm.

Halloysite nanotubes (HNTs) have been extensively investigated for potential utilization due to their unique structure and properties as a type of natural, eco-friendly clay. The synthesis and modification of magnetic halloysite nanotubes was studied using several experimental techniques including SEM, TEM, FT-IR, Raman spectroscopy, UV-Vis spectroscopy, and BET. Dye absorption experiments were conducted to understand bonding using EDS, XPS, XRD, and Raman spectroscopy. In this study, we evaluated Sunset Yellow FCF (SY) dye removal as a model to understand bonding structures among magnetic HNTs, magnetic particles, and dye molecules. We focus on the interactions of SY-magnetic HNTs and characteristics of magnetization by VSM after SY dye adsorption, which highlight the notable features of magnetic halloysite nanotubes. We used different pH environments to study the behavior of magnetic HNTs after dye absorption. The application of these modified HNTs is promising for future organic dye removal and wastewater treatment.

Cell membrane potential affects the electrostatic self-assembly of magnetizable nanoparticles around the flagellum of sperm cells, leading to the formation of biohybrid microrobots (i.e., IRONSperm) with various bending stiffness. Here we explain the influence of bull sperm cell membrane potential on the formation of two types of IRONSperm samples that are produced by electrostatic self-assembly. The first type is a proximal-coated soft body with nanoparticles concentrated on the head to maintain high flexibility of the flagellum and create a passively propagating transverse bending wave under the influence of an external rotating magnetic field. The second type is a rigid-body with nanoparticles approximately uniformly distributed along the length to provide arbitrary geometry that maintains a constant chiral shape and propel by rotation about its long axis. We present a magneto-elastohydrodynamic model to predict the swimming speed at low Reynolds number for rigid IRONSperm with arbitrary shapes, and show that decreasing the bending stiffness allows the model to capture the behavior of its soft counterpart. While the response of a rigid chiral IRONSperm is distinguished by a greater swimming speed with a smooth decay with frequency, the benefit of a soft flagellum in certain scenarios would present a much smaller range of frequencies for wireless actuation.