Abstract
Magnetization reversal of high aspect ratio truncated conical nanotubes of maximum radius 50 nm and height \(1~ \mu m\) is investigated as a function of tapering by micromagnetic modelling. Reversal of magnetization proceeds through nucleation of domain walls originating at the ends of tube. For near cylindrical tube, the remanent state exhibits core free vortex configurations with opposite chiralities on the extreme ends whilst a ferromagnetic ordering persists in the middle of the tube. As the radius of tube is reduced below 25 nm at one end, the vortex state is replaced by a flower configuration at that end. Analytical modelling of energy reinstates that the observed remanent states are energetically ground states. Angular dependence of coercivity shows a initial increase up to a critical angle showing a Kondorsky-type behaviour. Beyond the critical angle, a sharp fall in coercivity is noticed, which is modelled analytically using Stoner-Wohlfarth model.
Graphical Abstract
