Mössbauer measurements reveal four inequivalent Fe sites in ferrihydrite produced by Klebsiella oxytoca. The origin of these sites can be understood in terms of two nanosized structural regions in the bacterium and a certain ordering of bilayers and single layers of Fe-occupied octahedra.

We have studied the crystal structure and magnetic properties of Fe-containing nanoparticles formed as a result of microbial metabolism. Our experimental data, coupled with earlier results, suggest that the nanoparticles consist of ferrihydrite, Fe₂O₃ · nH₂O, and are in a superparamagnetic state.

Magnetic properties of multilayers, consisting of nanogranular (Co40Fe40B20)50(SiO2)50 layers as thin as magnetic granule diameter alternating the α-Si:H or SiO2 layers and the single layer film (Co40Fe40B20)50(SiO2)50 with the thickness much larger than the magnetic granule diameter are reported and compared. The thick single layer film is ferromagnetic but the multilayer film with the ultrathin granular layers and SiO2 spacer is superparamagnetic. This is interpreted as the result of increasing percolation threshold in the 2D granular media above 50% concentration of magnetic granules in the multilayer with the nonmagnetic and dielectric SiO2 spacer. The multilayer with the α-Si:H spacer is superparamagnetic at 300 K but it becomes ferromagnetic, when temperature is below 250 K. It is assumed to be resulted from the exchange interaction of magnetic granules through the semiconductor α-Si:H layers. The value of exchange interaction through the semiconductor spacer is estimated.

Magnetometry and ferromagnetic resonance are used to quantitatively study magnetic anisotropy with an easy axis both in the film plane and perpendicular to it. In the study of single-layer and multilayer permalloy films, it is demonstrated that these methods make it possible not only to investigate the average field of perpendicular and in-plane anisotropy, but also to characterize their inhomogeneity. It is shown that the quantitative data from direct integral and local measurements of magnetic anisotropy are consistent with the direct and indirect estimates based on processing of the magnetization curves. The possibility of estimating the perpendicular magnetic anisotropy constant from the width of stripe domains in a film in the transcritical state is demonstrated. The average in-plane magnetic anisotropy field of permalloy films prepared by magnetron sputtering onto a Corning glass is almost unchanged with the thickness of a single-layer film. The inhomogeneity of the perpendicular anisotropy field for a 500 nm film is greater than that for a 100 nm film, and for a multilayer film with a total permalloy thickness of 500 nm, it is greater than that for a homogeneous film of the same thickness.

The characteristic modification of the spectrum of the exchange spin waves has been revealed in ferromagnet/ferromagnet multilayer films with a thickness of N(d ₁ + d ₂) by the spin-wave resonance method. This modification is due to the first bandgap at the wavenumber k _b = π/(d ₁ + d ₂) of a magnon crystal, which is formed by one-dimensional modulation of the magnetization. It has been shown that the transformation of the multilayer film with thermal annealing to the film of a single-phase alloy is accompanied by the disappearance of this modification of the spectrum.

Ferrihydrite nanoparticles formed as a result of the microorganism activity have been studied using Mössbauer spectroscopy, X-ray powder diffraction analysis, and X-ray fluorescence analysis. Three po