Results 1 - 10 of 1754
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[en] Using full micromagnetic simulations we calculate the spectra of ferromagnetic resonance (FMR) for an iron (core-shell) nanocube and show that the FMR characteristics are strongly size dependent. For instance, for a 40 nm it is found that, in contrast to a macrospin picture, the spectrum of the iron nanocube possesses two bands centered around T and T. The peaks originate from the surface anisotropy induced by the strong demagnetizing fields (DMFs) of iron. Further simulations reveal that for nm nanocubes the macrospin model becomes viable. Above 40 nm we find a broad band for FMR absorption. Our results point to possible interpretations of existing FMR experimental observations for the system studied here.
[en] We analyse the ferromagnetic resonance that can be obtained in thin ferromagnetic films that present a mixture of biaxial and uniaxial anisotropy in the plane of the films. The d.c. and h.f. fields are situated in the plane of the films, perpendicular to each other and making different angles with the anisotropy axes. The equilibrium positions of the magnetization vector are calculated for different orientations of the film. The expressions for the resonance frequencies and the width of the resonance line for the case of a d.c. field applied along two easy axes of magnetization are given. The results that we obtained were particularized for the films with pure biaxial anisotropy. (author)
[en] The basic features of time-delayed feedback schemes for the control of chaos are reviewed. The method is applied to high-power ferromagnetic resonance experiments in YIG spheres beyond the Suhl threshold. Chaotic motion is suppressed, and regular periodic states are stabilized
[en] The dynamical properties of saturated spherical shells are investigated in the exchange-dominated regime when assuming that surface anisotropy is present at both the inner and outer boundaries. It is found that surface anisotropy plays an important role in determining the dependence of lower-order eigenvalues on shell thickness. The mode frequency can increase with decreasing shell thickness, or is driven rapidly towards the ferromagnetic resonance frequency depending on the choice of the surface anisotropy constant at each boundary. The presence of surface anisotropy significantly modifies the size dependence of the modes which can be suppressed or amplified based on the coupling between boundaries. When surface anisotropy is present only on the outer boundary, similar behaviour to the solid sphere is observed for lower-order eigenvalues up to a thickness of after which large deviations begin to occur, where and are the inner and outer radius, respectively. Moreover, surface anisotropy introduces a dependence of the zeroth mode on shell thickness, removing the degeneracy with the ferromagnetic resonance and leading to a pronounced size dependence of this mode for thin shells. (paper)
[en] An elaborate lineshape analysis of the ferromagnetic resonance (FMR) spectra taken in the temperature range 113K to 323K on nanocrystalline gadolinium shows that the complex temperature variation of the anisotropy field in bulk single crystal Gd still plays a decisive role in determining the magnetic properties of Gd in nanocrystalline form. The unusually broad FMR linewidth arises from nearly random variation of the easy direction of magnetization from grain to grain as well as from the magnetic inhomogeneities at the grain boundaries. The scaling equation of state analysis reveals a reduced value of the Curie temperature compared to that of the bulk. (author)
[en] The realization of negative permeability of an array of ferrite rods and the influencing factors are presented. The negative permeability is realized around the ferromagnetic resonance frequency of ferrite, and a tunable electromagnetic band gap is observed in the array of ferrite rods. The electromagnetic property of the array of ferrite rods is dominated by the unit's characteristics, including the dimension of the rods, but is insensitive to the structure parameters, such as spacing distance and duty ratio, which indicates that the array is a metamaterial, not a photonic crystal. Metamaterials with multi-band gaps are made using an array with different ferrite rods.
[en] The crystallization of metalic glasses METGLAS 2826 and METGLAS 2826A was investigated by ferromagnetic resonance. The line width of the absorption curve first derivative was measured for various isothermic treatment times at 3750C. It was observed that after the reduction atributed to tension relaxation, the line width increases with time treatment. The results suggest that, for suficiently long times, the line width is a function only of the transformed fraction. (A.C.A.S.)
[pt]A cristalizacao dos vidros metalicos METGLAS 2826 e METGLAS 2826A foi investigada por ressonancia ferromagnetica. A largura de linha da primeira derivada da curva de absorcao foi medida para varios tempos de tratamento isotermico a 3750C. Observou-se que apos uma diminuicao, atribuida a relaxacao de tensoes, a largura de linha passa a aumentar com o tempo de tratamento. Os resultados sugerem que, para tempos suficientemente longos, a largura de linha e funcao apenas da fracao transformada. (autor)
[en] In order to express the history of magnetization process dependence on ferromagnetic resonance (FMR) for a particle system we use a statistical model based on the Preisach model. The precedent magnetization processes define in Preisach plane a configuration of particle magnetization orientations. The particles are considered single domain and saturated and are modeled as Stoner-Wohlfarth particles. The FMR response of the system is computed by summarizing the individual dynamic susceptibility of the particles, keeping account of the initial directions of the particle magnetizations. The FMR spectra of the particle system is determined considering three initial magnetization states: the demagnetized state, the positive saturated state in which all the particles have the magnetization in the static field direction and the negative saturated state when all the particles have the magnetization in the opposite field direction. The static field dependence of the resonance frequency and linewidth are determined as functions of the initial magnetization states
[en] Both frequency swept and field swept ferromagnetic resonance measurements have been carried out for a number of different samples with negligible, moderate and significant extrinsic frequency independent linewidth contribution to analyze the correlation between the experimentally measured frequency and field linewidths. Contrary to the belief commonly held by many researchers, it is found that the frequency and field linewidth conversion relation does not hold for all cases. Instead it holds only for samples with negligible frequency independent linewidth contributions. For samples with non-negligible frequency independent linewidth contribution, the field linewidth values converted from the measured frequency linewidth are larger than the experimentally measured field linewidth. A close examination of the literature reveals that previously reported results support our findings, with successful conversions related to samples with negligible frequency independent linewidth contributions and unsuccessful conversions related to samples with significant frequency independent linewidth. The findings are important in providing guidance in ferromagnetic resonance linewidth conversions. (paper)