Banca de DEFESA: JADSON TADEU SOUZA DANTAS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : JADSON TADEU SOUZA DANTAS
DATE: 31/07/2020
TIME: 14:00
LOCAL: Plataforma Google Meet
TITLE:

Vortex Stabilization in Coupled Cylindrical Ferromagnetic Nanostructures

KEY WORDS:

magnetic vortex, magnetic nanostructure, dipolar interaction

PAGES: 130
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

Great discoveries in fundamental research very often lead to a new technology era. This is about to happen in nanomagnetism. Currently, there are promising perspectives of micro-wave nanoantenna’s design, based on the use of systems consisting of soft ferromagnetic nanoelements suitably designed to hold interacting magnetic vortices. Besides, there are demands for controlling the vortices chiralities. Experimental reports indicate that the vortex pair excitation spectra and magnetoresistance depend on the vortices chiralities. Furthermore, the synchronization of the vortex’s dynamics, owing to vortices interaction, leads to high-quality microwave spectra, with narrow emission lines, as desired for nanoantennas. The vortex magnetic profile results from a competition between the trends imposed by the exchange and the dipolar energies. Nanostructuring brings new elements and promising perspectives of tailoring the vortex magnetic profile of soft ferromagnetic nanoelements to suit device application demands. Placing two nanoelements together, if the nanoelements distance is comparable to its own geometrical dimensions, one may modify the intrinsic vortex profile of the soft material, because the dipolar field in each nanoelement may have a considerable contribution emanating from the other nanoelement. 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, and the uniaxial anisotropy easy axis in the plane of the circular faces. In addition, we have investigated similar Py systems for comparison purposes. 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 nanoelements, as required for device applications. Furthermore, we have shown that the vortices chiralities and locations in the nanocylinders may be controlled by using external fields of moderate strength. For circular nanocylinders pairs, we have used preparations routes with the external field-aligned either in the x-axis direction, parallel the easy axis of the Fe uniaxial anisotropy, or in the y-axis direction, perpendicular to the easy axis of the Fe uniaxial anisotropy. We have shown that owing to the impact of the uniaxial anisotropy in the sequence of magnetic phases along either the x-axis or the y-axis preparation route, and the remnant state may be either a same chirality vortex pair or an opposite chirality vortex pair. In the case of Py nanocylinders, there is no uniaxial anisotropy. Our results show that for Py nanocylinder pairs, the magnetic pattern at remanence does not depend on the direction of the in-plane external field used in the preparation route. We notice that one may have surprising features from the dipolar interaction between the Fe nanoelements. For instance, we have found that isolated 21 nm height and 129 nm diameter Fe nanocylinders hold a vortex at remanence. However, contrary to intuition, coaxial pairs of these nanocylinders, placed one on top of the other at short distances, may display, instead, an almost uniform state at remanence. This might be valuable information for designing nano-oscillators based on pair of vortices. We have also investigated the remnant state of pairs of identical elliptical 25nm height Fe nanocylinders with face-to-face distance ranging from 20nm to 60nm. The Fe nanocylinders uniaxial anisotropy easy axis is in the plane of the elliptical faces pointing along the minor axis direction. To induce vortex nucleation, we have used the preparation route with the external field along the minor axis direction. We have shown that controlling the dipolar interaction strength by changing the elliptical nanoelements distance, one may design the magnetic structure of four interacting vortices at remanence. For instance, we investigated pairs of Fe (195 nm x 305 nm x 25 nm) nanocylinders, each with a 195 nm and 305nm long minor and major axes, respectively. The isolated Fe nanocylinders hold a single vortex at the center at remanence. A pair of these nanocylinders, with a 35 nm face-to-face distance, instead, shows a pair of opposite chirality vortices in each nanocylinder. We have shown that there are relevant changes in the strength of the dipolar and local fields, owing to the change of the magnetic structure that results from vortices motion. We suggest that this may affect the restoring torques for vortices oscillations around the equilibrium positions.

BANKING MEMBERS:
Presidente - 6345702 - ARTUR DA SILVA CARRICO
Externo à Instituição - FABIO HENRIQUE SILVA SALES - IFMA
Externo à Instituição - LEONARDO LINHARES OLIVEIRA - UERN
Externa à Instituição - MARIA DAS GRACAS DIAS DA SILVA - UERN
Externo ao Programa - 3107198 - SERGIO MURILO DA SILVA BRAGA MARTINS JUNIOR