arXiv subjects

Peter Dunne

Publications and source records attributed to Peter Dunne.

6 recordsLinked to original sources

arXiv2024

Scaling and flow profiles in magnetically confined liquid-in-liquid channels

Ferrofluids kept in place by permanent magnet quadrupoles can act as liquid walls to surround a second non-magnetic inside, resulting in a liquid fluidic channel with diameter size ranging from mm down to less than 10 micrometer. Micro particle tracking velocimetry (micro PTV) experiments and modeling show that near ideal plug flow is possible in such liquid-in-liquid channels due to the reduced friction at the walls. The measured fluids velocity profiles agree with the predictions of a hydrodynamic model of cylindrical symmetry with a minimal set of hypotheses. By introducing symmetry breaking elements in the system, we show how unique velocity and flow properties can be obtained. Our liquid-in-liquid confinement opens new possibilities for < 10 micrometer-sized microfluidics with low pressures and low shear, with flow characteristics not attainable in comparable solid-wall devices.

physics.flu-dyn↗

arXiv2023

Roadmap for focused ion beam technologies

The focused ion beam (FIB) is a powerful tool for the fabrication, modification and characterization of materials down to the nanoscale. Starting with the gallium FIB, which was originally intended for photomask repair in the semiconductor industry, there are now many different types of FIB that are commercially available. These instruments use a range of ion species and are applied broadly in materials science, physics, chemistry, biology, medicine, and even archaeology. The goal of this roadmap is to provide an overview of FIB instrumentation, theory, techniques and applications. By viewing FIB developments through the lens of the various research communities, we aim to identify future pathways for ion source and instrumentation development as well as emerging applications, and the scope for improved understanding of the complex interplay of ion-solid interactions. We intend to provide a guide for all scientists in the field that identifies common research interests and will support future fruitful interactions connecting tool development, experiment and theory. While a comprehensive overview of the field is sought, it is not possible to cover all research related to FIB technologies in detail. We give examples of specific projects within the broader context, referencing original works and previous review articles throughout.

physics.ins-det↗

arXiv2023

Deterministic multi-level spin orbit torque switching using He+ microscopy patterning

He$^+$ ion irradiation is used to pattern multiple areas of Pt/Co/W films with different irradiation doses in Hall bars. The resulting perpendicular magnetic anisotropy landscape enables selective multilevel current-induced switching, with full deterministic control of the position and order of the individual switching elements. Key pattern design parameters are specified, opening a way to scalable multilevel switching devices.

cond-mat.mes-hall↗

arXiv2022

Dynamic Analysis of Confined Ionic Liquids and Ionic Magnetic Fluids: Highlighting Long Range Elastic Interactions

By reinforcing the interaction energy of the liquid with respect to the surface using total wetting boundary conditions, the response of liquids to mechanical shear stress is stronger and exhibits at sub-millimeter scale elastic properties. This study extends here to liquids with strong electrostatic interactions such as ionic liquids and paramagnetic liquids. We show that it is also possible to identify and measure a non-zero low-frequency shear elasticity at sub-millimeter scale. The observation of mesoscopic elastic properties in liquids generally considered as viscous away from any phase transition and the absence of extended structuring confirm the relevance of considering elastic interactions as contributing to collective effects under external electric or magnetic field.

cond-mat.soft↗

arXiv2021

Fluid drag reduction by magnetic confinement

The frictional forces of a viscous liquid flow are a major energy loss issue and severely limit microfluidics practical use. Reducing this drag by more than a few tens of percent remain illusive. Here, we show how cylindrical liquid-in-liquid flow leads to drag reduction of 60-99% for sub mm and mm sized channels, irrespective of whether the viscosity of the transported liquid is larger or smaller than that of the encapsulating one. In contrast to lubrication or sheath flow, we do not require the continuous flow of the encapsulating lubricant, here made up of a ferrofluid held in place by magnetic forces. In a laminar flow model with appropriate boundary conditions, we introduce a modified Reynolds number with a scaling that depends on geometrical factors and viscosity ratio of the two liquids. It explains our whole range of data and reveal the key design parameters for optimizing the drag reduction values. Our results therefore open the route to microfluidics designs with pressure gradients possibly reduced by orders of magnitudes.

physics.app-ph↗

arXiv2020

Helium Ion Microscopy for Reduced Spin Orbit Torque Switching Currents

Spin orbit torque driven switching is a favourable way to manipulate nanoscale magnetic objects for both memory and wireless communication devices. The critical current required to switch from one magnetic state to another depends on the geometry and the intrinsic properties of the materials used, which are difficult to control locally. Here we demonstrate how focused helium ion beam irradiation can modulate the local magnetic anisotropy of a Co thin film at the microscopic scale. Real-time in-situ characterisation using the anomalous Hall effect showed up to an order of magnitude reduction of the magnetic anisotropy under irradiation, and using this, multi-level switching is demonstrated. The result is that spin-switching current densities, down to 800 kA cm$^{-2}$, can be achieved on predetermined areas of the film, without the need for lithography. The ability to vary critical currents spatially has implications not only for storage elements, but also neuromorphic and probabilistic computing.

cond-mat.mes-hall↗