Physicists develop new method to visualize magnetic nanostructures with high resolution

November 20, 2024 by Martin Luther University Halle-Wittenberg

Collected at: https://phys.org/news/2024-11-physicists-method-visualize-magnetic-nanostructures.html

A new method enables researchers to analyze magnetic nanostructures with a high resolution. It was developed by researchers at Martin Luther University Halle-Wittenberg (MLU) and the Max Planck Institute of Microstructure Physics in Halle.

The new method achieves a resolution of around 70 nanometers, whereas normal light microscopes have a resolution of just 500 nanometers. This result is important for the development of new, energy-efficient storage technologies based on spin electronics. The team reports on its research in the current issue of the journal ACS Nano.

Normal optical microscopes are limited by the wavelength of light and details below around 500 nanometers cannot be resolved. The new method overcomes this limit by utilizing the anomalous Nernst effect (ANE) and a metallic nano-scale tip. ANE generates an electrical voltage in a magnetic metal that is perpendicular to the magnetization and a temperature gradient.

“A laser beam focuses on the tip of a force microscope and thus causes a temperature gradient on the surface of the sample that is spatially limited to the nanoscale,” says Professor Georg Woltersdorf from the Institute of Physics at MLU. “The metallic tip acts like an antenna and focuses the electromagnetic field in a tiny area below its apex.”

Physicists develop new method to visualize magnetic nanostructures with high resolution — (a) Schematic illustration of the ANE imaging method. The VANE is given by the transverse component of the magnetization shown by the orange arrow and the vertical temperature gradient shown by the red arrow. (b) Line scan of VANE across a device of width w = 10 μm in a field of 40 and −40 mT. The device is illuminated by a 5 mW laser beam with a wavelength of 532 nm focused by a 60× (NA = 0.7) objective. The inset shows a schematic of the device structure utilized for the measurements. (c,d) Kerr and SANE microscopy images of multidomain states stabilized in different device structures as indicated with the schematics. Credit: ACS Nano (2024). DOI: 10.1021/acsnano.4c09749

This enables ANE measurements with a much better resolution than conventional light microscopy allows. The microscopic images published by the research team achieve a resolution of around 70 nanometers.

Previous studies have only investigated magnetic polarization in the sample plane. However, according to the research team, the in-plane temperature gradient is also crucial and allows to probe the out-of-plane polarization using ANE measurements. In order to close this gap and demonstrate the reliability of the ANE method for visualizing magnetic structures on the nanometer scale, the researchers used a magnetic vortex structure.

A particular advantage of the new technique is that it also works with chiral antiferromagnetic materials.

“Our findings are significant for the thermoelectric imaging of spintronic components. We have already demonstrated this with chiral antiferromagnets,” says Woltersdorf.

“With our method has two advantages: on the one hand, we have greatly improved the spatial resolution of magnetic structures, far beyond the possibilities of optical methods. Secondly, it can also be applied to chiral antiferromagnetic systems, which will directly benefit our planned Cluster of Excellence Centre for Chiral Electronics.”

More information: Atul Pandey et al, Anomalous Nernst Effect-Based Near-Field Imaging of Magnetic Nanostructures, ACS Nano (2024). DOI: 10.1021/acsnano.4c09749

Journal information: ACS Nano

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