We develop a new approach in magneto-optical imaging (MOI), applying for the first time a ghost imaging (GI) protocol to perform Faraday microscopy. MOI is of the utmost importance for the investigation of magnetic properties of material samples, through Weiss domains shape, dimension and dynamics analysis. Nevertheless, in some extreme conditions such as e. g. cryogenic temperatures or high magnetic fields application, there exists a lack of domains images due to the difficulty in creating an efficient imaging system in such environments. Here we present an innovative MOI technique that separates the imaging optical path from the one illuminating the object. The technique is based on thermal light GI and exploits correlations between light beams to retrieve the image of magnetic domains. As a proof of principle, the proposed technique is applied to the Faraday magneto-optical observation of the remanence domain structure of an yttrium iron garnet sample.
Samples composed of a polymer matrix were loaded with different fractions from 0% to 30% of Fe oxide magnetic nanoparticles with an average size ranging from 5 to 25 nm. The permittivity and permeability of the composites were determined upon a very wide frequency range, spanning from DC to 30 GHz using different methods with overlapping frequency intervals. The nanoparticle content was observed to significantly modify the permeability and permittivity behavior of the polymer. The frequency and intensity of both dielectric and ferromagnetic resonances of the composites are clearly affected by the presence of the magnetic nanoparticles, and the composites can be optimized for specific applications requiring absorption of electromagnetic radiation from the MHz to the GHz range.
The superior high-frequency magnetic behavior of transverse anisotropy amorphous ribbons can be qualitatively interpreted in terms of rotation dominated magnetization process and quantitatively predicted describing the spin dynamics by the Landau-Lifshitz-Gilbert (LLG) equation in association with the electromagnetic diffusion equation. The theory is applied to comprehensive measurements performed on Co-based alloys, tested as field-annealed tapewound rings from dc to 1 GHz with combination of fluxmetric and transmission line methods. The LLG equation is numerically solved considering the role of magnetostatic, exchange, anisotropy, eddy current, and applied fields. It accurately describes the high-frequency energy losses, ensuing from eddy currents, and spin damping. By further considering the low-frequency domain wall contribution, a full scenario for the broadband losses is achieved.
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