Ferromagnetic resonance studies of amorphous and nanocrystalline FeCuNbSiB alloys

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Abstract
Alloys with composition Fe 73.5 Cu 1 Nb 3 Si 22.5−x B x , where x=6 and 9, have been studied from the as-cast state, through various stages of crystallization, in annealing range of 300–650 °C, by the technique of ferromagnetic resonance (FMR). The annealing was performed isothermally at preset temperatures to produce nanocrystallinestructures in an amorphous matrix. Both the nanocrystallinestructures and the surrounding amorphous matrix are ferromagnetic, and will therefore contribute to the FMR spectra. The spectral features, resonance field, intensity, and linewidth have been used to characterize the structurally related changes in the sample during the crystallization process. The major changes in the spectra are observed to occur in the region of the crystallization peak in the differential thermal analysis curves for these samples. The FMR spectra exhibit a complex in-plane angular variation, which is understood in terms of preferential orientation of the magnetization vector in the direction of the ribbon, and shape effects. The square cut samples give rise to multipeaked spectra when the external magnetic field is applied in an “off-square” direction. This is the first report of the appearance of a second resonance feature of this type. This is explained as arising from the magnetic confinement of the nanocrystallites in the amorphous matrix, producing spin waves localized at the interface of the two phases.