APS March Meeting 2023
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session S54: Nanomagnetic Systems: From Spin Textures to Topological Structures
8:00 AM–10:12 AM,
Thursday, March 9, 2023
Room: Room 306
Chair: Anish Rai, University of Delaware
Abstract: S54.00001 : 3D vector nanoimaging of spin textures in nanostructured magnetic materials*
8:00 AM–8:36 AM
Understanding topological spin configurations is of paramount importance because of scientific interests and practical applications. Examples of topological spin texture include magnetic Skyrmions and topological magnetic monopoles (TMMs). TMMs are also known as magnetic hedgehogs or Bloch points, which are 3D nonlocal spin textures robust to thermal and quantum fluctuations due to their topology. However, observing the magnetization of TMMs directly and mapping out their interactions at tens of nanometer scales has been challenging – this is due to the lack of high-resolution, non-destructive 3D imaging techniques that can penetrate relatively thick samples. Here, we report the creation of more than 100 stable TMMs in a frustrated ferromagnetic meta-lattice, which is made of silica nanospheres and infiltrated nickel between the spheres. These field-free room temperature TMMs do not possess strong anisotropy or the Dzyaloshinskii-Moriya interaction. The complex 3D curved surfaces of the nanospheres in the meta-lattice create a magnetically frustrated configuration harboring topological spin textures. We further developed a new imaging technique called "3D soft x-ray vector ptychography" to determine the magnetization and emergent magnetic fields of the TMMs with a 3D spatial resolution of 10 nm. This new imaging method utilizes x-ray magnetic circular dichroism, ptychography, scalar and vector tomography, to quantitatively image and reconstruct nanoscale spin textures. The achieved resolution is comparable to the magnetic exchange length of transition metals, enabling us to study monopole-monopole interactions. We observed that TMMs with opposite charges are separated closer than those with the same charges, indicating that the system is near equilibrium. In summary, our work demonstrates that magnetic meta-lattices could be used as a new platform to create and investigate the interactions of TMMs. Furthermore, we expect soft x-ray vector ptychography to be applied broadly to quantitatively image 3D vector fields in magnetic and anisotropic nanomaterials based on facility-scale (synchrotrons) and table-top scale (laser-driven high harmonic generation) x-ray sources.
*This work is supported by STROBE: a National Science Foundation Science & Technology Center (DMR 1548924).