Navegando por Autor "Rezende, S. M."
Agora exibindo 1 - 6 de 6
- Resultados por página
- Opções de Ordenação
Artigo Angular dependence of hysteresis shift in oblique deposited ferromagnetic/ antiferromagnetic coupled bilayers(AIP Publishing LLC, 2014-07-17) Oliveira, Alexandre Barbosa de; Rodrigues-Suarez, R. L.; Michea, S.; Vega, H.; Azevedo, A.; Rezende, S. M.; Aliagla, Carolina; Denardin, J.The angular dependence of the hysteresis shift has been investigated in ferromagnetic/antiferromagnetic (NiFe/IrMn) bilayers grown by oblique deposition under the influence of a static magnetic field applied perpendicular to the uniaxial anisotropy direction induced during the growth process. It was found that at low oblique deposition angles, the unidirectional anisotropy field is much greater than the uniaxial anisotropy field and the corresponding anisotropies directions are noncollinear. In these conditions, the angular dependence of the hysteresis loop shift exhibits the well know cosine like shape but demanding a phase shift. Contrary to this, at high oblique deposition angle (70), the uniaxial anisotropy plays the fundamental role and the anisotropies directions are collinear. In this case, the exchange bias displays a jump phenomenon. The numerical calculations are consistent with the experimental data obtained from magneto-optical Kerr effect and ferromagnetic resonance.Artigo Critical thickness investigation of magnetic properties in exchange-coupled bilayers(American Physical Society, 2011-06-24) Oliveira, Alexandre Barbosa de; Rodrigues-Suárez, R. L.; Vilela-Leão, L. H.; Bueno, T.; Almeida, J. R. L.; Landeros, P.; Rezende, S. M.; Azevedo, A.We present a systematic investigation of the magnetic properties of two series of polycrystalline ferromagneticantiferromagnetic bilayers (FM-AF) of Ni81Fe19(10nm)/Ir20Mn80(tAF) grown by dc magnetron sputtering. One series was grown at an oblique angle of 50◦ and the other one was grown at 0◦. Ferromagnetic resonance (FMR) was used to measure the exchange bias field HE, the rotatable anisotropy field HRA, and the FMR linewidth H as a function of the antiferromagnetic layer thickness tAF. Three relaxation channels due to isotropic Gilbert damping, anisotropic two-magnon scattering, and mosaicity effects are simultaneously distinguished through the angular dependence of the FMR linewidth. In the regime of small IrMn layer thicknesses, not enough to establish the exchange bias anisotropy, the FMR linewidth shows a sharp peak due to the contribution of the two-magnon scattering mechanism. The results presented here are of general importance for understanding the dynamics of magnetization in the FM-AF structures.Artigo Mössbauer study of spin-glass Fe x Zn1−x F2 system(Hyperfine Interaction, 1991-11) Araújo, Jose Humberto de; Cunha, Joao Batista Marimon da; Vasquez, A.; Amaral, L.; Moro, J. T.; Montenegro, F. C.; Rezende, S. M.; Coutinho-Filho, Mauricio D.57Fe Mössbauer effect measurements in the diluted Ising antiferromagnet Fe x Zn1−x F2 withx=0.25 andx=0.57 at temperatures between 4.2 and 55 K, are reported. DC suceptibility measurements show a spin-glass (SG) phase at low temperatures forx≤0.31. Our Mössbauer spectra show a phase transition to a SG state with antiferromagnetic order (AFSG) forx=0.25 and only antiferromagnetic order forx=0.57.Artigo Rotatable anisotropy on ferromagnetic/antiferromagnetic bilayer investigated by Brillouin light scattering(AIP Publishing, 2018-01-23) Oliveira, Alexandre Barbosa de; Rodrigues-Suarez, R. L.; Estrada, F.; Maior, D. S.; Arana, M.; Santos, O. Alves; Azevedo, A.; Rezende, S. M.The nature of the rotatable anisotropy in ferromagnetic/antiferromagnetic (FM/AF) NiFe/IrMn bilayers has been investigated using magneto-optical Kerr effect magnetometry, ferromagnetic resonance, and Brillouin Light Scattering (BLS) techniques. The behavior of the magnon frequencies with an external magnetic field applied in the bilayer plane has been measured by BLS. The angular dependence of magnon frequency shows a shift when compared to numerical calculation for different magnetic field intensities. This frequency shift can be associated with the rotatable anisotropy and it depends on the magnetic field intensity. As a result, the rotatable anisotropy field exhibits a non-monotonic dependence on the applied field. The results are interpreted considering the coexistence of parallel and antiparallel coupling at the FM/AF interface.Artigo Spin freezing of the spin-glass Fe0.25Zn0,75F2: a Mossbauer study(Brazil Journal Physics, 1991-01) Araújo, José Humberto de; Cunha, Joao Batista Marimon da; Vasquez, Adalberto; Montenegro, F. C.; Rezende, S. M.; Amara, Lovelyn; Moro, J. T.; Coutinho-Filho, Mauricio D.We report 57~e Mõssbauer measurements in the diluted Ising antiferromagnet Fe0.25Zn0,75F2 at temperatures between 4.2 and 28 K. DC susceptibility measurements in the same sample show a spin-glass phase at a freezing temperature Tg = 10K. We found that for this concentration there is a competitive coexistence of spin-glass behaviour and antiferromagnetic order. The freezing temperature is frequency-dependent and follows a power lawArtigo Thickness dependence of the magnetic anisotropy and dynamic magnetic response of ferromagnetic NiFe films(IOP Publishing, 2017-04-03) Silva, Edimilson Félix da; Corrêa, Marcio Assolin; Pace, R. D. Della; Cid, C. C. Plá; Kern, P. R.; Carara, M.; Feitosa, Carlos Chesman de Araújo; Santos, O. Alves; Rodríguez-Suárez, R. L.; Azevedo, A.; Rezende, S. M.; Bohn, FelipeWe investigate the thickness dependence of the magnetic anisotropy and dynamic magnetic response of ferromagnetic NiFe films. We go beyond quasi-static measurements and focus on the dynamic magnetic response by considering three complementary techniques: the ferromagnetic resonance, magnetoimpedance and magnetic permeability measurements. We verify remarkable modifications in the magnetic anisotropy, i.e. the well-known behavior of in-plane uniaxial magnetic anisotropy systems gives place to a complex magnetic behavior as the thickness increases, and splits the films in two groups according to the magnetic properties. We identify magnetoimpedance and magnetic permeability curves with multiple resonance peaks, as well as the evolution of the ferromagnetic resonance absorption spectra, as fingerprints of strong changes of the magnetic properties associated to the vanishing of the in-plane magnetic anisotropy and to the emergence of non-homogeneous magnetization configuration, local anisotropies and out-of-plane anisotropy contribution arisen as a consequence of the non-uniformities of the stress stored in the film as the thickness is increased and/or to the columnar growth of the film. We interpret the experimental results in terms of the structural and morphological properties, quasi-static magnetic behavior, magnetic domain structure and different mechanisms governing the magnetization dynamics at distinct frequency ranges