Estabilização de vórtices em nanoestruturas ferromagnéticas acopladas

Abstract

There are currently promising perspectives of micro-wave nanoantenna’s architecture, consisting of ferromagnetic nanoelements suitably designed to hold vortices. Experimental reports indicate that the excitation spectra and the magnetoresistance of a pair of magnetic vortices may be affected by their dipolar interaction. Furthermore, the dipolar interaction may affect the synchronization of the pair of vortices dynamics, leading to high-quality microwave spectra. Placing two soft ferromagnetic nanoelements close to each other, one may control the strength of the dipolar interaction between them, and produce changes in the vortex profiles. We have investigated the magnetic structure at remanence of pairs of vortices of a pair of identical and coaxial 21 nm height Fe circular nanocylinders with the diameter ranging from 81 nm to 129 nm. We have shown that by choosing appropriate values of the nanocylinders distance, one may control the dipolar interaction strength, allowing to set the relative chirality of the vortices in pairs of circular Fe and Py nanocylinders. We have also shown that the vortices chiralities and locations in the nanocylinders may be controlled by using external magnetic fields. We have used two preparations routes, one with the external field-aligned along the x-axis direction, parallel the easy axis of the Fe uniaxial anisotropy, and another with the external field along the y-axis direction. We have shown that the remnant state may be either a same chirality vortex pair or a pair of vortices with opposite chiralities. We have also investigated the remnant state of pairs of identical elliptical 25nm height Py nanocylinders with face-to-face distance ranging from 20nm to 60nm. Owing to the shape anisotropy, there are considerable differences of the sequence of magnetic phases formed along the preparation routes with the external parallel to the major axis or to the minor axis. Our results indicate that controlling the dipolar interaction and the shape anisotropy, one may design the magnetic structure of four interacting vortices at remanence. For both the circular and elliptical nanocylinder systems, there are relevant changes in the strength of the dipolar and local fields, owing to the change of vortex positions in response to external magnetic fields of moderate strength. We suggest that this may be used to design strongly synchronized multiple vortices nano-oscillators with high quality spectra