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The giant magnetoimpedance (GMI) and giant stress impedance (GSI) behaviors of amorphous ribbons composed of three commercially available materials (Co66Si15B14Fe4Ni1, Fe81B13Si3.5C2, and Ni40Fe40Si + B19Mo1−2) with differing saturation magnetostriction constants (λ s) and Young's moduli (E) were studied under longitudinal stress/strain. The linearity of the ribbons' GSI responses and gauge factors was measured to create a figure of merit and compare their stress/strain sensing performance for strains up to ɛ = 10 × 10−3. We observed that the Ni40Fe40Si + B19Mo1−2 ribbon displayed the best performance for low strains (ɛ < 1 × 10−3), whereas the Co66Si15B14Fe4Ni1 ribbon displayed the best performance for higher strains (ɛ < 10 × 10−3). We conclude that the suitability of a material for sensing strains in any given strain regime has a complex dependence on both λ s and E, the former of which dictates both the absolute magnitude of the impedance variation materials exhibit (i.e., the dynamic range), while both λ s and E control how their impedances vary with applied strain. [ABSTRACT FROM AUTHOR]

Domain walls (DWs) in magnetic nanowires are promising candidates for a variety of applications including Boolean/unconventional logic, memories, in-memory computing as well as magnetic sensors and biomagnetic implementations. They show rich physical behaviour and are controllable using a number of methods including magnetic fields, charge and spin currents and spin-orbit torques. In this review, we detail types of DWs in ferromagnetic nanowires and describe processes of manipulating their state. We look at the state of the art of DW applications and give our take on the their current status, technological feasibility and challenges. [ABSTRACT FROM AUTHOR]

We have investigated the pinning and depinning of "virtual" domain walls in planar magnetic nanowires. Such virtual walls are created when a conventional domain wall becomes annihilated at a narrow gap between two segments of a discontinuous nanowire. By using focused magneto-optical Kerr effect magnetometry to study the repeatability of their depinning, we show that virtual walls exhibit single-mode depinning distributions, characterized by remarkably low, sub-Oersted standard deviations. This is in stark contrast to the depinning of domain walls from conventional notch-shaped defects, which typically exhibit multi-mode depinning field distributions spanning tens to hundreds of Oersteds. High-resolution magnetic soft x-ray microscopy measurements are used to reveal that this high level of repeatability is the result of a simple mediated-nucleation process, which decouples the depinning mechanism from structure of the initially injected DWs. Our work serves as an example of how the complex and dynamical stochastic behaviors exhibited by domain walls in nanowires can be controlled. [ABSTRACT FROM AUTHOR]

We have used the results of micromagnetic simulations to investigate the effects of nanowire geometry and domain wall magnetization structure on the characteristic parameters of magnetic atom traps formed by domain walls in planar ferromagnetic nanowires. It is found that when traps are formed in the near-field of a domain wall both nanowire geometry and wall structure have a substantial effect on trap frequency (how tightly atoms are spatially confined) and adiabaticity (how closely the atoms' magnetic moments track the applied field direction within the trap). We also show that in certain regimes a trap's depth depends only on the amplitude of an externally applied rotating magnetic field, thus allowing it to be tuned independently of the trap's other critical parameters. [ABSTRACT FROM AUTHOR]

A design of a biological molecule carrier is presented for the application of high throughput multiplexing biological assays. This carrier contains a bit addressable “magnetic barcode” made of either Permalloy or cobalt thin films, sandwiched between two planar SU8 protective layers. We describe how the design of the magnetic carriers is optimized by engineering the coercivity of each barcode element, allowing the number of available signatures to be increased. Fully encapsulated digital magnetic carriers which carry a 5 bit addressable barcode were also fabricated and are presented. Writing and reading of digital carriers were both performed after releasing in dried solution. [ABSTRACT FROM AUTHOR]

The dependence of the exchange bias field and coercivity enhancement on ferromagnetic (FM) and antiferromagnetic (AF) layer thickness in exchange biased bilayers has been systematically investigated in CoFe/FeMn and CoFe/PdMn bilayers for digital encoding applications in biotechnology. A magnetic multilayer structure can be used as a digitally encoded tag if each (bi)layer has two magnetic states, positive and negative saturation, available at remanence and if each layer can be uniquely identified by its coercivity. We will demonstrate that by adjusting the AF and FM layer thickness in an AF/FM bilayer, both the bias field and the coercivity of the bilayer can be controlled. By contrasting CoFe/FeMn bilayers with CoFe/PdMn bilayers, it becomes apparent that the relative magnitudes of the coercivity enhancement and bias field depend on the particular AF material, although the qualitative behavior remains unchanged. In order to create a multilayer that can retain one of many magnetic states at remanence, a large coercivity enhancement but absent or small bias field are preferred. Analysis of the bilayers suggest that PdMn is a better choice of AF layer for this purpose and results on some multilayer films are shown which validate this claim. [ABSTRACT FROM AUTHOR]

The magnetic properties and magnetoresistance of thin-film circular and elliptical magnetic rings made from Co, NiFe, NiFe/FeMn, and Co/Cu/NiFe have been explored. Single-layer rings show stable onion and vortex states and metastable twisted states containing a 360° wall. For NiFe rings, four-point magnetotransport results can be explained quantitatively by anisotropic magnetoresistance. NiFe/FeMn exchange-biased rings show offset hysteresis loops, and the easy axis is determined by a combination of the ring ellipticity and the exchange coupling. In Co/Cu/NiFe multilayer rings the behavior is dominated by the magnetostatic coupling between the domain walls in the Co and NiFe. In the major loop the giant magnetoresistance varies between three distinct levels corresponding to combinations of onion and vortex states in the NiFe and Co layers. [ABSTRACT FROM AUTHOR]

The magnetization reversal of individual 2 μm and 5 μm diameter polycrystalline Permalloy rings, with respective widths 0.75 μm and 1 μm, thickness 45 nm, has been investigated by focused magneto-optic Kerr effect (MOKE) magnetometry. Micromagnetic simulation of the reversal in the 2 μm diameter ring reveals that the onion-to-vortex state switching occurs by nucleation and subsequent annihilation of vortex walls that span the width of the ring, and that the vortex-to-reverse-onion state switching occurs by expansion of a reverse domain. The hysteresis loop shows good agreement with the experimental MOKE loop. Measurements of the switching through one-half of a 5 μm diameter ring enable the determination of the circulation of the vortex states accessed during one applied field cycle. The rings switch via one vortex state (either clockwise or anticlockwise) on both downward and upward applied field sweeps. The number of applied field cycles spent switching via one vortex state before changing to switch via the opposite vortex state is random, likely to be due to the history of the spin configuration and thermal fluctuations. [ABSTRACT FROM AUTHOR]

Microarrays and suspension-based technologies have attracted significant interest over the past decade with applications in medical diagnostics and biochemical multiplexed assays. However, the throughput of microarrays will always be limited by the array density and the slow kinetics, while the suspension (or bead)-based technologies are currently limited by the number of distinct codes the beads can carry. A novel digital magnetic tagging technology based on magnetic tags that can be used as encoded microcarriers for biomolecular probes, is presented here. The highly disruptive platform technology can provide a very large number of unique codes, enabling a high degree of multiplexing. The design principles of a novel magnetic laboratory-on-a-chip device comprising microfluidic channels with embedded magnetic tunneling magnetoresistive sensors are also discussed. [ABSTRACT FROM AUTHOR]

The low temperature magnetic switching behavior of micron scale NiFe/Cu/Co circular ring elements has been investigated using micromagnetic simulations and magnetoresistance (MR) measurements. The rings were patterned, so that two different contact configurations could be used to measure MR simultaneously. By comparing these measurements with the simulation results, the rings’ magnetization states and switching routes were determined at both 1.7 and 300 K. It was found that at 1.7 K the rings exhibited multiple switching routes and also showed more metastable states and broader transitions between states than was observed at 300 K. The rings’ behavior at low temperature is explained as the result of an increase in the strength of magnetocrystalline and magnetoelastic anisotropies combined with an absence of thermal excitation which would usually aid the nucleation and depinning of domain walls. [ABSTRACT FROM AUTHOR]

Microarrays and suspension (or bead)-based technologies have attracted significant interest for their broad applications in high throughput molecular biology. However, the throughput of microarrays will always be limited by the array density and the slow diffusion of molecules to their binding sites. Suspension-based technologies, in which all the reactions take place directly on the surface of microcarriers functionalized with molecular probes, could offer true multiplexing due to the possibility of extending their detection capability by a straightforward expansion of the size of the chemical library of probes. To fully exploit their potential, the microcarriers must be tagged, but the number of distinct codes available from spectrometric/graphical/physical encoding methods is currently fairly limited. A digital magnetic tagging method based on magnetic microtags, which have been anisotropy engineered to provide stable magnetization directions which correspond to digital codes, is reported. The tags can be suspended in solution and functionalized with a variety of biological molecular probes. Magnetic tagging offers several benefits compared to the traditional optical encoding techniques currently employed. It offers minimal background signals, potential for a large number of distinct codes, miniaturization of devices, and the ability to write a code in situ. Experimental data showing the reading of individual magnetic microbars from samples comprising 50×20 μm2 Ni elements, as well as micromagnetic simulations that show the feasibility of stray field detection, are presented. The stray fields of the magnetic microbars spanning a range of 60 mOe were detected by a microfabricated fluxgate sensor scanned in a raster fashion over the sample that was placed about 70 μm away. Free floating tags have also been fabricated for use in microfluidic systems. A magnetic lab-on-a-chip device could be used for tagging biomolecular probes for applications in genome sequencing, immunoassays, clinical diagnostics, drug discovery, and general pathogen detection and screening. [ABSTRACT FROM AUTHOR]