Abstract
Magnetic vortex-based media have recently been proposed for several applications of nanotechnology; however, because lithography is typically used for their preparation, their low-cost, large-scale fabrication is a challenge. One solution may be to use arrays of densely packed cobalt nanowires that have been efficiently fabricated by electrodeposition. In this work, we present this type of nanoscale magnetic structures that can hold multiple stable magnetic vortex domains at remanence with different chiralities. The stable vortex state is observed in arrays of monocrystalline cobalt nanowires with diameters as small as 45 nm and lengths longer than 200 nm with vanishing magnetic cross talk between closely packed neighboring wires in the array. Lorentz microscopy, electron holography and magnetic force microscopy, supported by micromagnetic simulations, show that the structure of the vortex state can be adjusted by varying the aspect ratio of the nanowires. The data we present here introduce a route toward the concept of 3-dimensional vortex-based magnetic memories.
Highlights
IntroductionMagnetic vortices are objects of rotational symmetry composed of a relatively small core (typically < 10 nm), where the magnetization points out of the sample plane, surrounded by in-plane (e.g., circumferential) magnetization[1,2]
Magnetic vortices are objects of rotational symmetry composed of a relatively small core, where the magnetization points out of the sample plane, surrounded by in-plane magnetization[1,2]
Cylindrical NWs with diameters between 15–200 nm and high aspect ratios can be prepared by electrodeposition into templates
Summary
Magnetic vortices are objects of rotational symmetry composed of a relatively small core (typically < 10 nm), where the magnetization points out of the sample plane, surrounded by in-plane (e.g., circumferential) magnetization[1,2]. The practical realization of these applications will depend on the ability to create low-cost, large-scale media that have a high density of magnetic elements with dimensions down to a few 10ths of a nm and that have a stable vortex state Such planar structures can be integrated into potential new spintronic devices using well-established electron beam lithography; this restricts structures to the existing 2-dimensional device paradigm. We report the first direct experimental proof of the existence of stable magnetic vortex states at remanence in cylindrical, single-crystal hcp Co NWs by Lorentz microscopy (LorTEM) and electron holography Using this system, we are able to present a 3D concept of magnetic vortex media for multiple applications in nanotechnology
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