Operando control of skyrmion density in a Lorentz transmission electron microscope with current pulses

Abstract

Magnetic skyrmions hold promise for spintronic devices. To explore the dynamical properties of skyrmions in devices, a nanoscale method to image spin textures in response to a stimulus is essential. Here, we apply a technique for operando electrical current pulsing of chiral magnetic devices in a Lorentz transmission electron microscope. In ferromagnetic multilayers with interfacial Dzyaloshinskii-Moriya interaction (DMI), we study the creation and annihilation of skyrmions localized by point-like pinning sites due to defects.Using a combination of experimental and micromagnetic techniques, we establish a thermal contribution for the creation and annihilation of skyrmions in our study. Our work reveals a mechanism for controlling skyrmion density, which enables an examination of skyrmion magnetic field stability as a function of density. We find that high-density skyrmion states are more stable than low-density states or isolated skyrmions resisting annihilation over a magnetic field range that increases monotonically with density.

Visibility and Apparent Size of Néel-Type Magnetic Skyrmions in Fresnel Defocus Images of Multilayer Films

“…One possible approach for subtracting the non-magnetic background is to increase the applied magnetic field to saturate the magnetic moments in the sample and to record and subtract the corresponding image (see, for example, Park et al, 2020). However, this approach requires the alignment of the resulting images, taking into account changes in rotation and magnification due to the different excitation of the objective lens (see Supplementary Information 3).…”