Abstract
Abstract Multilayers that comprise thin films of heavy metals and ferromagnets have been shown to host Néel-type magnetic skyrmions at room temperature. Fresnel defocus imaging in Lorentz transmission electron microscopy is a widely used technique for recording magnetic information about skyrmions. However, the visibility of Néel-type skyrmions in Fresnel defocus images is typically low, both because only a small component of their magnetic field contributes to the signal and because of the presence of diffraction contrast from the polycrystalline multilayer structure. Here, we take advantage of the out-of-plane hysteresis in such samples to record background-subtracted Fresnel defocus images. We demonstrate an improvement in magnetic signal-to-noise ratio and spatial resolution by a factor of 3 for a (Pt/Co/NiFe)×5 multilayer. We also use simulated Fresnel defocus images of Néel-type magnetic skyrmions to understand the influence of defocus on apparent skyrmion size.
Highlights
Magnetic skyrmions are whirl-like spin textures, which are foreseen as elementary building blocks in future low-power storage and logic devices (Nagaosa & Tokura, 2013; Fert et al, 2017)
We demonstrate an improvement in magnetic signal-to-noise ratio and spatial resolution by a factor of 3 for a (Pt/Co/NiFe)×5 multilayer
In zero applied magnetic field, the Fresnel defocus image shows black and white curved lines, which result from the presence of magnetic domains separated by domain walls
Summary
Magnetic skyrmions are whirl-like spin textures, which are foreseen as elementary building blocks in future low-power storage and logic devices (Nagaosa & Tokura, 2013; Fert et al, 2017). Stacks of thin layers of heavy metals and ferromagnets with the DMI at their interfaces (Bogdanov & Rößler, 2001) have been shown to host magnetic skyrmions at room temperature (Jiang et al, 2015; Boulle et al, 2016; Moreau-Luchaire et al, 2016; Woo et al, 2016). Magnetic interactions in such stacks can be tuned by changing the compositions of the layers, thereby providing control over magnetic skyrmion size and density (Soumyanarayanan et al, 2017). Magnetic imaging techniques with high spatial resolution and sensitivity are, required to investigate small magnetic skyrmions
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