Operando Control of Skyrmion Density in a Lorentz Transmission Electron Microscope with Current Pulses

The demonstration of sub-100 nm magnetic skyrmions at room temperature in ferromagnetic multilayers raises the realistic possibility of implementing skyrmion device technology. The key to this effort is understanding the stability and behavior of skyrmions on this scale. We study the response of skyrmions to external stimuli such as magnetic field and electric current pulses by fabricating a device compatible with operando current pulsing in a Lorentz transmission electron microscope. We investigate the behavior of skyrmions that are strongly bound to magnetic pinning sites using this method. While the pinning sites obstruct the skyrmions' motion, we observe that skyrmions are created and deleted by current pulses. Our investigation of the skyrmion density over a range of current pulse energies and magnetic fields reveal that we can control skyrmion density with current pulses. We use micromagnetic simulation to clarify the mechanism of thermally assisted skyrmion nucleation and annihilation. Finally, we show that high density skyrmion states are more stable over the magnetic field perturbation than isolated skyrmion states through the suppression of stretching of skyrmions into stripe domains at low magnetic fields.