Control of Vortex Structures in Individual Cylindrical Magnetic Nanowires by Simultaneous Action of Applied Magnetic Field and an Electric Current

Abstract

Cylindrical magnetic nanowires (CNWs) are promising candidates for the building blocks of 3D information technologies such as shift registers, magnetic recording, spintronics and logic gates1-4. Spin-polarized-current is an energy efficient way to excite magnetization dynamics in planar nanostructures. However, in CNWs this research is doing its first steps5. Magnetization dynamics in a CNW of Permalloy, 100 nm diameter and 1 µm length, is investigated under simultaneous application of electric current and magnetic field by micromagnetic simulations. The magnetization reversal process initiates with the creation of open vortex structures with different rotation senses at the nanowire ends. We conclude that the electric current by itself enlarges or reduces the length of these vortex structures according to the rotational sense of the associated Oersted field. Large enough current densities produce a vortex structure which covers the whole nanowire surface. At the same time, the magnetization in the very core of the nanowire remains the same, i.e. no complete magnetization reversal is possible in the absence of external magnetic field. The simultaneous action of the applied electric current and magnetic field allows the complete control of the vortex structures in terms of setting the polarity and vorticity. The resulting diagram of magnetic states obtained after the application of field and electric current showing the values required for the vorticity and axial magnetization switching is presented in Figure 1. This control is essential for future information technologies based on 3D vertical nanostructures. The presented state diagram will become useful for future experiments on current-induced domain wall dynamics in CNWs.