Project Report

Electron microscopy is a widely used tool to characterize materials at the nanometer scale (billionth of a meter). Electrons are accelerated towards a sample and then scatter when they come in come contact. Various detectors and instrumental setups can be used to obtain structural, crystallographic, and even magnetic domain structure information. Lorentz transmission electron microscopy allows us to visualize the in-plane magnetic domain structure of thin samples by measuring the deflection of an incident electron beam on a thin magnetic sample. This technique has most recently been implemented to observe exotic magnetic domains in spiral (helimagnetic) and vortex (Skyrmion) configurations. These magnetic configurations arise due to chiral magnetic interactions which only appear for certain crystal systems, and in the case of this work we look specifically at cubic systems that have no center of inversion symmetry. The Skyrmion domain configurations have special topological properties that essentially allow the spin configuration to act as a mobile magnetic particle which could have possible uses for magnetic storage applications. In this work, we sought to observe Skyrmion magnetic domains in nanowire (thin rod-shaped) samples to understand the effects of size confinement on exotic magnetic domains. We developed several sample preparation methods to observe the nanowires in a Lorentz electron microscope. The sample preparation techniques focused on creating thin cross-sections of nanowires with large diameters so that the microscope could more easily observe the magnetic domain structure. We found that the surface roughness intrinsic to the nanowires as well the cylindrical geometry of nanowires made it difficult to observe the magnetic domain structure. Despite the initial lack of evidence for helimagnetic or Skyrmion magnetic domains, this first attempt at observation of nanowires by Lorentz electron microscopy has helped reveal the stringent requirements for the successful observation of magnetic domain structure in nanowire samples and will help guide future work in this area.

National Science Foundation (NSF)
Office of International and Integrative Activities (IIA)
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Carter Kimsey
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United States
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