Physicists have developed a method for accurately capturing magnetic nanostructures.

The resolution of conventional optical microscopes is limited by the wavelength of light, which makes objects smaller than 500 nanometers indistinguishable.

A methodology developed by researchers from Martin Luther University in Halle-Wittenberg (MLU) and the Max Planck Institute for Microstructure Physics in Germany overcomes this limitation. Physicists utilized the anomalous Nernst effect (ANE) and a specialized nanoscale metallic tip of the microscope probe to achieve high resolution.

The anomalous Nernst effect generates an electric voltage in a magnetic material that is perpendicular to both the magnetization and the temperature gradient in the sample. The researchers determined that this could be harnessed.

The scientists had to simultaneously heat as small an area of the sample as possible while creating an electromagnetic field in the same region. Under these conditions, the ANE generates a voltage, which the researchers measured to create images by correlating all the data from the examined area.

“We were able to focus a laser beam on the tip of an atomic force microscope cantilever, thus creating a temperature gradient on the surface of the sample confined to a nanoscale area. The metallic tip acted as an antenna, concentrating the electromagnetic field in a tiny area beneath its tip,” explains Professor Georg Woltersdorf (Georg Woltersdorf).

This technique allows for measurements of ANE with much higher resolution than what is possible with traditional optical microscopy. The research group demonstrated images obtained using the new method with a resolution of approximately 70 nanometers.

Previous studies focused only on magnetic polarization within the plane of the sample. However, according to the research group, the temperature gradient in the plane is also crucial and enables the investigation of out-of-plane polarization through ANE measurements. To address this gap and showcase the reliability of the ANE method for visualizing magnetic structures at the nanoscale, the researchers employed a magnetic vortex structure.

A magnetic vortex is a configuration of magnetic moments in a material where the directions of magnetization twist around a central point, forming a vortex distribution.

A significant advantage of the new technique is that it can be used with chiral antiferromagnetic materials. This special class of magnetic materials has atomic magnetic moments organized antiparallel, as in typical antiferromagnets, but also exhibits chirality—twist or asymmetry in their magnetic structure. Chiral antiferromagnets are being actively researched for applications in spintronics, quantum electronics, and sensing, making it essential for scientists to observe objects made from these materials in detail.

The work has been published in the journal ACS Nano.