SPICE Workshop on Nanomagnetism in 3D, April 30th - May 2nd 2024
Charudatta M Phatak
There has been growing interest in three dimensional (3D) nanoscale magnetic structures that can host topologically non-trivial spin textures. This is because of fundamental interest in understanding and controlling such spin textures and their interactions as well as their potential technological applications. In order to understand and harness the behavior of such novel magnetic nanostructures, it is imperative to gain a quantitative understanding of the local energy landscape as a function of their shape and geometry. For example, interplay between extrinsic factors such as shape anisotropy and intrinsic factors such as magnetocrystalline anisotropy can lead to emergence of novel spin textures.
However, there are several challenges associated with exploring the behavior of magnetic nanostructures whether in two-dimensional continuous thin films [1] , or patterned at nanoscale such as artificial spin ices [2], or three-dimensional (3D) such as nanohelices [3]. Since the magnetic fields are 3D in nature, understanding their effect is of critical importance for magnetic imaging since the quantity being imaged is typically a projection of the true vector field. For example, in Lorentz transmission electron microscopy (LTEM), we observe the projected magnetic induction, which not only includes the contribution from magnetization inside the sample but also the stary field outside the sample. This can result in misinterpretation of the LTEM images [4]. Combining the experimental observations with micromagnetic simulations can give a better understanding of the spin textures as well as give insight into their energetics.
In this presentation, we will discuss the frontiers of imaging and understanding the spin textures in nanomagnetic systems using LTEM. We will present our framework, PyLorentz, that can be used for quantitative imaging of 2D and 3D nanostructures including cobalt nanohelices. We will show how the magnetization distribution is affected by the geometry of the nanostructures. Finally, we will also present a new method for extending the existing capabilities to direct imaging of 3D magnetization using LTEM [5].
References
[1] A.R.C. McCray, et al. Nano Lett. 22(19), 7804–7810 (2022).
[2] T. Cote, A.K. Petford-Long, and C. Phatak, Nanoscale 15(27), 11506–11516 (2023).
[3] J. Fullerton, A.R.C. McCray, A.K. Petford-Long, and C. Phatak, Nano Lett., (2024).
[4] A.R.C. McCray, T. Cote, Y. Li, A.K. Petford-Long, and C. Phatak, Physical Review Applied 15(4), 044025 (2021).
[5] A.R.C. McCray, M. Cherukara, A.K. Petford-Long, and C. Phatak, Microscopy and Microanalysis 29(S1), 1756–1757 (2023).
[6] This work was supported by U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02- 06CH11357.