In situ magnetic field dependent Lorentz microscopy in Co nanowires grown by focused electron beam induced deposition

Abstract

The accurate characterization and control of the magnetic configuration in nanostructures, namely domain walls (DWs) or vortex structures, by external parameters such as the magnetic field is essential for applications such as information storage, sensing or magnetic logic. Transmission electron microscopy (TEM) allows the observation of the magnetic nanostructures with nanometer-range spatial resolution by Lorentz microscopy (LM). In this work, we performed in situ characterization and magnetic-field manipulation of DWs by LM in Co nanowires (NWs) in a FEI Titan Cube 60-300 TEM. These NWs were fabricated by focused electron beam induced deposition (FEBID) with purity higher than 90% on Si3N4 membranes. We determined the nucleation and propagation field of DWs by direct observation of the magnetic structure by LM of curved L-shape Co NW with varying width (w=125-1000 nm) and thickness (t=5-30 nm), demonstrating that for specific dimensions they are good DW propagators. Focal series in LM were acquired in order to map the in-plane magnetic induction by solving the Transport-of-Intensity Equation. The nucleation process gives rise to transversal DW in the thinner NWs (t < 13 nm). Above this value, the crossover to complex structures was investigated, including multiple vortex walls on the thicker NWs.