Probing magnetic structure at the nanoscale with local thermal flow injection

Magnetic imaging is a key tool when building microelectronic devices, as understanding the magnetic structure and properties of a given material determines its applications. For instance, ferromagnetic and antiferromagnetic Weyl semimetals have unique magnetic properties that could make them useful candidates in spintronic applications. As these devices grow increasingly smaller, spatial resolution becomes an increasingly important property of magnetic imaging technologies.

Budai et al. demonstrated high-resolution magnetic imaging through heat injection with an atomic force microscope (AFM). The team tested their method on the ferromagnetic Weyl semimetal Co₂MnGa and reported a spatial resolution in the sub-100 nanometer range. This technique is simpler to implement, using a standard cantilever instead of the specialized cantilever found in scanning thermal microscopes.

“AFM tip contact on the sample surface locally induces a heat flow injection, and the local anomalous Nernst effect (ANE) creates an electric field that is orthogonal to both the heat flow and the magnetization,” said author Hironari Isshiki. “Therefore, magnetic imaging is possible by mapping the ANE voltage across the sample while scanning the tip on the sample surface with contact mode.”

They plan to expand their work by increasing the sensitivity of the method and employing it to study the magnetic structure of antiferromagnetic Weyl semimetals.

“The magnetic structure in the domain wall of antiferromagnetic Weyl semimetals has not been clarified and must be investigated,” said Isshiki. “According to theories, the width of the magnetic domain wall is expected to be approximately 1 micrometer. Thus, magnetic imaging with high spatial resolution is crucial to study these interesting materials.”

Source: “High-resolution magnetic imaging by mapping the locally induced anomalous Nernst effect using atomic force microscopy,” by Nico Budai, Hironari Isshiki, Ryota Uesugi, Zheng Zhu, Tomoya Higo, Satoru Nakatsuji, and YoshiChika Otani, Applied Physics Letters (2023). The article can be accessed at https://doi.org/10.1063/5.0136613 .