Direct Experimental Observation of 3D Vortex States in Multilayer Fe/Gd using Scanning Electron Microscopy with Polarization Analysis (SEMPA)

Abstract

The global market for power solely for data center usage is estimated to be $12.4 billion by 2027[1]. In 2021, data center electricity consumption was ∼400 TW h, representing almost 2% of the global energy demand[2]. Ongoing efforts in spintronics, which use spin currents instead of traditional charge currents at a fraction of the power[3], are paving the way for significant savings, both financially and environmentally. There has been considerable research into alternatives for memory[4–6] including a magnetic structure known as a skyrmion, a self-supporting magnetic texture characterized by a non-trivial topology. Recent advances in creating room-temperature stable skyrmions has reignited interest in these objects.

Building on previous work in the McMorran group, this research set out to build a more complete understanding of the 3D structure of metastable magnetic skyrmions, specifically in Fe/Gd thin films. This was done using traditional trans- mission electron microscope (TEM) techniques along with a unique scanning elec- tron microscope with polarization analysis at the University, the SEMPA. Data col- lected using a TEM in Lorentz mode, providing information integrated through the bulk of the material, was combined with data from SEMPA, providing surface- sensitive information about the top of the material. Analysis of the data suggests atopologically complex winding nature for the magnetization of skyrmions in this material.

Presented herein is a brief introduction of the magnetic structures found in Fe/Gd multilayer thin films; an analysis using new analytical tools built for this purpose of the data collected; and a user’s manual for SEMPA, including mainte- nance and troubleshooting guidance.