Direct Observation of Unconventional Topological Spin Structure in Coupled Magnetic Discs

Phatak, Charudatta; Petford‐Long, Amanda K.; Heinonen, Olle

doi:10.1103/physrevlett.108.067205

Cited by 77 publications

(49 citation statements)

References 23 publications

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“…The experimental contrast is however lower than expected in theory, which will be discussed in sec.IV. Of importance is the fact that the lateral scale of the wire is expanded by a factor 1/ sin (16 • ) ≈ 3.6 in the shadow, thanks to the grazing incidence. In princi- ple this promises an increase of spatial resolution of 3.6 along one direction, however issues of signal-over-noise ratio may limit this gain, which will be addressed in the next section.…”

Section: B Experimental Test Cases: Curling Structuresmentioning

confidence: 99%

“…The modeled wire is suspended above the surface, so that the entire shadow is visible. Note that the lateral scale is expanded by a factor sin (16 • ) ≈ 3.6 in the shadow, thanks to the grazing incidence.…”

Section: Comparison With Experimentsmentioning

confidence: 99%

“…While coupled nanocubes had been imaged by electron holography in the case of parallel cores [14], stacked disks could be imaged recently with magnetic tomography holography, revealing fine details in the case of (repulsive) antiparallel cores [15]. The topological identity of such structures with so-called merons has been highlighted [16]. Another example is long and cylindrical nanowires and nanotubes [17], which in a dense array would be the natural geometry to implement a 3D race-track magnetic memory [18].…”

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confidence: 99%

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Quantitative analysis of shadow x-ray magnetic circular dichroism photoemission electron microscopy

et al. 2015

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Shadow X-ray Magnetic Circular Dichroism Photo-Emission Electron Microscopy (XMCD-PEEM) is a recent technique, in which the photon intensity in the shadow of an object lying on a surface, may be used to gather information about the three-dimensional magnetization texture inside the object. Our purpose here is to lay the basis of a quantitative analysis of this technique. We first discuss the principle and implementation of a method to simulate the contrast expected from an arbitrary micromagnetic state. Text book examples and successful comparison with experiments are then given. Instrumental settings are finally discussed, having an impact on the contrast and spatial resolution : photon energy, microscope extraction voltage and plane of focus, microscope background level, electric-field related distortion of three-dimensional objects, Fresnel diffraction or photon scattering.Progress is continuous in the decreasing size and increasing complexity of nanosized magnetic systems being designed for either fundamental science or devices. Magnetic microscopies are crucial tools to monitor and understand the properties of such systems. Various types of information are desirable to gather, leading to multiple criteria to classify microscopies: spatial and time resolution, compatibility with environmental parameters such as variable temperature and applied magnetic field, requirements on the sample preparation and compatibility for ex-situ processing such as lithography, correlation with structural information, elemental sensitivity, quantity measured (magnetization, induction, stray field etc.), sensitivity. The most common magnetic microscopies offering spatial resolution below 50 nm and direct sensitivity to magnetization are X-ray Magnetic Circular Dichroism PhotoEmission Electron Microscopy (XMCD-PEEM) [ [7][8][9].Yet another criterion is the volume of the sample probed. This criterium is gaining in importance in the context of the emergence of three-dimensional (3D) magnetic objects and textures. The distribution of magnetization may be truly 3D if along the three directions in space the size of a system lies above magnetic characteristic length scales, such as the dipolar exchange length ∆ d for soft magnetic materials, or the anisotropy exchange length ∆ u for a hard magnetic material [10]. While this is obviously fulfilled in macroscopic materials, the complexity of magnetic textures is such that it cannot be measured in detail, and besides it cannot be controlled to achieve specific functions. The progress in nanofabrication techniques now allows to design suitable systems, both with top-down and bottom-up approaches. Let us give some examples. Flat magnetic elements are basic building blocks in spintronics, being patterned with great 2D versatility with thin film and lithography technologies. Large lateral dimensions may give rise to 2D magnetic textures, such as the so-called vortex state in disks [11]. Such textures are being investigated to design RF oscillator components, relying on the gyrotropic motion ...

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Section: B Experimental Test Cases: Curling Structuresmentioning

confidence: 99%

Section: Comparison With Experimentsmentioning

confidence: 99%

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confidence: 99%

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Quantitative analysis of shadow x-ray magnetic circular dichroism photoemission electron microscopy

et al. 2015

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“…The magnetostatic problem is ubiquitous for any system that involves patterned micronor sub-micron size magnetic bodies, such as read or write heads in magnetic hard disk drives, magnetic nanoparticles 25 , coupled magnetic disks 26,27 , or artificial spin ices 28 . In patterned ferromagnetic systems, there typically arises a competition between the short-range exchange interactions and long-range magnetostatic interactions.…”

Section: B Magnetostatic Problemmentioning

confidence: 99%

An O(N) and parallel approach to integral problems by a kernel-independent fast multipole method: Application to polarization and magnetization of interacting particles

Jiang

Zhao

et al. 2016

The Journal of Chemical Physics

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we solve a boundary value problem for a ferroelectric/ferromagnetic volume in free space. In the second, we solve an electrostatic problem involving polarizable dielectric bodies in an unbounded dielectric medium. The results from these test cases show that our proposed parallel approach, which is built on a kernel-independent FMM, can enable highly efficient and accurate simulations and allow for considerable flexibility in a broad range of applications.

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“…For soft ferromagnetic disks and ferromagnetic coupling, the magnetization in the disks quite naturally is arranged in two vortices with the same sense of orientation, or chirality, and the same direction of the out-of-plane magnetization at the core (polarity). More suprisingly, a weakly antiferromagnetic coupling can lead to two antiferromagnetically arranged meron structures in the disks 26 , the stability of which is further enhanced by biquadratic coupling between the disks 24 . In this arrangement, the magnetization is out-of-plane at the center of the disks, just as for a vortex, and then radially outward in one disk, and inward in the other disk, except for near the edges, where the magnetization is arranged to close flux lines 6 .…”

Section: Introductionmentioning

confidence: 99%

Magnetization dynamics of coupled ferromagnetic disks

Heinonen

2015

Phys. Rev. B

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The magnetization configuration in two stacked micron-size ferromagnetic disks can assume different equilibrium states depending on the interfacial coupling between the disks. Here, I examine the magnetization dynamics in response to an out-of-plane field pulse for different equilibrium states. For antiferromagnetic coupling, the response spectrum generally consists of a lower-frequency part and a higher-frequency part. The former is related to the response of the core region, which has a significant in-plane response coupled to the out-of-plane one; the latter is related to spin waves generated at the edges of the disk. For a meron structure the response in the two disks to an out-of-plane pulse is also asymmetric.

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Direct Observation of Unconventional Topological Spin Structure in Coupled Magnetic Discs

Cited by 77 publications

References 23 publications

Quantitative analysis of shadow x-ray magnetic circular dichroism photoemission electron microscopy

Quantitative analysis of shadow x-ray magnetic circular dichroism photoemission electron microscopy

An O(N) and parallel approach to integral problems by a kernel-independent fast multipole method: Application to polarization and magnetization of interacting particles

Magnetization dynamics of coupled ferromagnetic disks

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