Using wideband (0.5–6.5 eV) spectroscopic ellipsometry, we study ultrathin [Bi(0.6–2.5 nm)–FeNi(0.8,1.2 nm)]N multilayer films grown by rf sputtering deposition, where the FeNi layer has a nanoisland structure and its morphology and magnetic properties change with decreasing the nominal layer thickness. From multilayer model simulations of the ellipsometric angles, Ψ(ω) and Δ(ω), complex (pseudo)dielectric function spectra of the Bi layer were extracted. The obtained results demonstrate that the Bi layer can possess the surface metallic conductivity, which is strongly affected by the morphology and magnetic properties of the nanoisland FeNi layer in GMR-type Bi–FeNi multilayer structures.
We study the phenomenon of optical nonreciprocity in multilayer systems of magnetic nanoislands [FeNi-AlO] . An anomalously large optical nonreciprocity was observed in these systems. The effect was manifested in nonequivalence of polarization plane rotation of reflected light for the sample in an initial position and rotated by [Formula: see text]. We assume that the super-vortex magnetization in the FeNi layers is responsible for the optical nonreciprocity effect. It was found that the value of nonreciprocity effect depends on the effective thickness of FeNi island layer and reaches a maximum with the super-vortex magnetization formation. The nonreciprocity magnitude is significantly higher than the values observed recently in systems of specially formed magnetic nanoparticles. Nonreciprocity magnitude is strongly dependent on interlayer interaction between nanoisland layers at large distances.
The results of studies of magnetization processes of multilayer structures, consisting of periodically alternating island layers of various magnetic materials, are presented. The unidirectional axis of magnetization, which does not lead to exchange bias of hysteresis loops, is found in these structures. A vortex-like type of magnetization of island structures, when the vortex magnetization is distributed on set of nanoislands, is proposed. Preliminary simulations and experiments on the effects of vortex magnetic field on island systems have shown that proposed vortex-like state can be implemented in multilayer island systems and can influence their magnetic structure.
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