Navegando por Autor "Oliveira, L. L."
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Artigo Dipolar field effects on the critical current for spin transfer switch of iron and permalloy nanoelements(AIP Publishing LLC, 2014-02-10) Carriço, Artur da Silva; Oliveira, L. L.; Dantas, J. T. S.; Dantas, Ana L.; Souza, R. M.We report a theoretical study of dipolar effects on the switching current density of soft ferromagnetic elliptical nanoelements. Relevant changes on the critical current value are found according to the orientation of the magnetization and the spin polarization with the major axis. We show that the critical current density may be reduced by as much as 92% for thin nanoelements magnetized along the minor axis direction, using in-plane spin polarization parallel to the magnetization.Artigo 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.Artigo Ferromagnetic resonance of compensated ferromagnetic/antiferromagnetic bilayers(AIP Publishing LLC, 2012-10-02) Carriço, Artur da Silva; Dantas, Ana L.; Oliveira, L. L.; Silva, M. L.We report a theoretical study of the ferromagnetic resonance (FMR) frequency Ω(H) of Fe/FeF2(110) and Fe/MnF2(110) uniaxial anisotropy compensated bilayers. We show that under external field perpendicular to the anisotropy axis, the uniform mode of the Fe-film becomes soft at an external field strength (H∗=HFA−H⊥int) smaller than the Fe anisotropy field. For strong interface exchange coupling, there is a gap in the FMR spectrum. In this case, Ω(H) is a monotonically increasing function of the external field strength and for any value of the external field strength Ω(H)>Ω(0). The value of the effective interface field downshifts (H⊥int) and the value of Ω(0) may be used to estimate the interface exchange energy.Artigo 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 deWe 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 nanoparticlesArtigo 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.Artigo Thermal hysteresis of ferromagnetic/antiferromagnetic compensated bilayers(Physical review B, 2009-10-12) Nascimento, F. I. F.; Dantas, Ana L.; Oliveira, L. L.; Mello, V. D.; Camley, R. E.; Carriço, Artur da SilvaWe report a theoretical investigation of thermal hysteresis of fourfold anisotropy ferromagnetic FM film exchange coupled to a compensated antiferromagnetic substrate. Thermal hysteresis occurs if the temperature interval includes the reorientation transition temperature, below which the frustration of the interface exchange coupling leads to a 90° rotation of the magnetization of the ferromagnetic layer. The temperature width of the thermal hysteresis is tunable by external magnetic fields of modest magnitude, with values of 43 K for an external field of 110 Oe and of 14 K for a field of 210 Oe, for a Fe 12 nm/MnF2 110 bilayer. For a Fe 3 nm/FeF2 110 bilayer the width of the thermal hysteresis is 23 K at 110 Oe and 13 K at 300 Oe. We discuss how the thickness of the iron film affects the field tuning of the thermal hysteresis width, and also how the thermal loops may be used to identify the nature of the interface exchange energy.