In Situ TEM Observation of Current-Induced Domain Wall Motion in Patterned Permalloy Wires

Using a transmission electron microscope (TEM) operating in Lorentz mode, we observe the movement of a domain-wall due to the flow of current in a permalloy wire. The wire is formed on electron-transparent silicon nitride membranes using standard electron beam lithography and thermal vacuum deposition. The resulting wire geometry is 30 nm thick, $\sim $100nm wide, and microns long. A custom-built electrical measurement stage and palladium leads deposited on top of the permalloy wires allow in situ measurements on the wire in the TEM. Lorentz mode imaging (Fresnel contrast) allows the determination of the domain wall location. We observe the domain wall to move in the direction of electron flow, with a current density of around 1 x 10$^{11}$ A/m$^{2}$ being required to move the wall. We will present the nanofabrication process, results, and interpretation of these experiments.