Navegando por Autor "Rebouças, G. O. G."

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Confinement of magnetic vortex and domain walls in dipolar coupled concentric nanocylinders
(IEEE, 2015-05) Carriço, Artur da Silva; Dantas, Ana L.; Rebouças, G. O. G.; Souza Júnior, I. D. Q.; Souza, C. M.; Oliveira, Leonardo L.; Nunes, Marcos S.
We report a theoretical study of the magnetic phases of core–shell nanocylinders, consisting of a Py cylindrical core, dipolar coupled to a coaxial Fe cylindrical shell. A few nanometers thick nonmagnetic cylindrical layer separates the core from the shell, and controls the magnitude of the core–shell dipolar interaction. New magnetic phases emerge from the dipolar interaction, and may consist of either the combination of the intrinsic magnetic phases or new phases that are not seen in isolated cylinders and shells. We discuss typical examples. The magnetic phases of a 21 nm-height nanocylinder composed of a 57 nm-diameter Py core coupled to a 12 nm-thick Fe shell may be set to be a Py vortex with the same chirality of the Fe shell circular state, or a Py uniform domain coupled to a pair of domain walls of the Fe shell onion state. A magnetic vortex may be stabilized in a 6 nm-height, 42 nm-diameter Py cylinder coupled to a 6 nm-thick Fe shell.
Controlling the core-to-core distance of vortex pairs in exchange-biased iron elliptical nanoelements
(AIP Publishing LLC, 2012-02-10) Carriço, Artur da Silva; Oliveira, Felipe F.; Moura, Thiago R. S.; Dantas, Ana L.; Rebouças, G. O. G.
We report a theoretical study of vortex pairs in exchange-biased elliptical iron nanoelements. We show that the remanent state may be tailored to fit vortex pairs with opposite chiralities separated by a diamond-like domain. Flat nanoelements with lateral dimensions ranging from 115 nm × 425 nm to 195 nm × 425 nm have the core-to-core distance tunable by the interface field strength.
Depinning field of a periodic domain wall array in vicinal nanowires
(Journal of Applied Physics, 2009) Dantas, Ana L.; Rebouças, G. O. G.; Carriço, Artur da Silva
We report a theoretical investigation of the magnetic states and depinning field of a periodic array of head-to-head domain walls of flat Fe rectangular nanowires, exchange coupled with a vicinal two-sublattice uniaxial antiferromagnetic substrate. We show that for strong interface exchange energy, domain walls are pinned at interface steps perpendicular to the antiferromagnetic easy axis, separating terraces with opposite interface exchange field. The array sequence, which alternates head-to-head and tail-to-tail domain walls, may form a structure with alternate chirality or with the same chirality. The domain wall dipolar field affects the chirality sequence, which is tunable by the geometrical constraints and the strength of the interface exchange field. The depinning field of 10 nm thick, 1 μm long wires, with widths of 100 and 200 nm, is of the order of the interface field strength, and the depinning process involves domain wall motion and the transversal displacement of a periodic array of vortices.
Excitations of interface pinned domain walls in constrained geometries
(AIP Publishing LLC, 2017-12-05) Carriço, Artur da Silva; Dantas, Ana Lucia; Martins, S. M. S. B.; Oliveira, L. L.; Rebouças, G. O. G.
We report a theoretical investigation of the equilibrium pattern and the spectra of head-to-head and Neel domain walls of flat Fe and Py stripes, exchange coupled with a vicinal antiferromagnetic substrate. We show that the domain wall excitation spectrum is tunable by the strength of the interface field. Furthermore, strong interface coupling favors localized wall excitations.
High-energy product SmCo5@Fe core-shell nanoparticles
(American Physical Society, 2018-04-16) Carriço, Arthur da Silva; Dantas, Ana Lucia; Oliveira, L. L.; Pedrosa, S. S.; Rebouças, G. O. G.; Silva, R. B.; Araújo, José Humberto de
We report a theoretical study of core-shell dipolar interaction effects on the energy product of hard/soft SmCo5@Fe core-shell spherical nanoparticles. We show that the impact of the core-shell dipolar interaction on the shell reversal process is tunable by the values of the core diameter and shell thickness. Maximum energy product optimization requires small core diameters, and the energy product enhancement may reach more than 370% for small core diameters SmCo5@Fe core-shell nanoparticles
Impact of core-shell dipolar interaction on magnetic phases of spherical core-shell nanoparticles
(American Physical Society, 2015-08-26) Carriço, Artur da Silva; Medeiros Filho, F. C.; Oliveira, L. L.; Pedrosa, S. S.; Rebouças, G. O. G.; Dantas, Ana L.
We show that confinement in small volumes affects the interplay of exchange and dipolar interactions and the magnetic phases of hard and soft spherical core-shell nanoparticles. Large variations in the magnetization of thin shells may occur due to the core dipolar field gradient within the shell. The reversal field is tunable by the trends imposed by the dipolar and core-shell interface exchange energies. We show, for instance, that the reversal field of a CoFe2O4 (30 nm)@ MnFe 2O4 (6 nm) particle ranges from 15.5 kOe for antiferromagnetic coupling down to 2.5 kOe for ferromagnetic coupling.
Interface roughness effects on coercivity and exchange bias
(Journal of Applied Physics, 2005) Dantas, Ana L.; Rebouças, G. O. G.; Silva, André S. W. T.; Carriço, Artur da Silva
We report model calculations of the hysteresis loops of exchange-coupled ferromagnet/antiferromagnet bilayers with monolayer-scale roughness and show that the loops are affected by the combined effect of the interface field strength, the degree of magnetic roughness and magnetostatic effects. The magnetization reversal may occur via domain-wall nucleation at the edges of monoatomic interface steps or coherent magnetization rotation. A magnetic phase diagram is constructed for a 10-nm-thick Fe film, subjected to nanometer-scale interface roughness.
Magnetic hysteresis of interface-biased flat iron dots
(Physical review B, 2009-03-04) Rebouças, G. O. G.; Silva, A. S. W. T.; Dantas, Ana L.; Camley, R. E.; Carriço, Artur da Silva
We report a theoretical study of the coercivity and bias of iron dots exchange coupled with an antiferromagnetic substrate. We show that flat dots, with height close to the iron exchange length, and lateral dimensions of a few exchange lengths, exhibit large enhancement of coercivity and exchange bias. For small interface field strength the magnetization reversal is nearly a coherent rotation with symmetrical loops. Interface pinning leads to large reduction in coercivity and asymmetrical loops, if the interface field strength is comparable to the value of the iron exchange field. We discuss the impact of geometrical confinement and interface pinning on the magnetization reversal mechanisms. We show that small area dots with height larger than the exchange length display stronger interface effects.
Nucleation of vortex pairs in exchange biased nanoelements
(American Institute of Physics, 2011-03-24) Carriço, Artur da Silva; Rebouças, G. O. G.; Dantas, Ana L.; Silva, A. S. M.
We report a theoretical investigation of interface effects in the magnetic order of interface biased iron and Permalloy™ elliptical nano-elements. Contrary to intuition, there is a partial pinning of the interface layer, favoring double vortex states along the hysteresis loop. Interface biasing affects the relative chirality and the distance of the vortices. Unbiased nanoelements may nucleate vortex pairs with the same chirality separated by an antivortex. For interface biased nanoelements the vortex pair forms with opposite chirality separated by a magnetic domain.

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Navegando por Autor "Rebouças, G. O. G."