The fall of a magnet through a hollow conducting tube is described. Although this experiment is well known, a detailed treatment by means of a circuit analysis allows us to relate the conductivity of the tube to the characteristic parameters of the experiment.

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Dipolar interactions on magnetic nanowire arrays have been investigated by various techniques. One of the most powerful techniques is the ferromagnetic resonance spectroscopy, because the resonance field depends directly on the anisotropy field strength and its frequency dependence. In order to evaluate the influence of magnetostatic dipolar interactions among ferromagnetic nanowire arrays, several densely packed hexagonal arrays of NiFe nanowires have been prepared by electrochemical deposition filling self-ordered nanopores of alumina membranes with different pore sizes but keeping the same interpore distance. Nanowires’ diameter was changed from 90 to 160 nm, while the lattice parameter was fixed to 300 nm, which was achieved by carefully reducing the pore diameter by means of Atomic Layer Deposition of conformal Al2O3 layers on the nanoporous alumina templates. Field and frequency dependence of ferromagnetic resonance have been studied in order to obtain the dispersion diagram which gives information about anisotropy, damping factor, and gyromagnetic ratio. The relationship between resonance frequency and magnetic field can be explained by the roles played by the shape anisotropy and dipolar interactions among the ferromagnetic nanowires.

A procedure has been developed to obtain the two-magnon linewidth contributions in single and polycrystalline ferrites in which, working with ferrimagnetic resonance experiments, the applied field was only slightly larger than the value required to saturate the sample. This theory has been shown to work in manganese ferrites. Single-crystal MnFe 2 O 4 has been prepared by the floating-zone technique and polycrystalline ferrite by the ceramic method. The spinel structure and composition have been confirmed by x-ray and inductively coupled plasma spectrometry, respectively. Fitting of the experimental ferrimagnetic resonance linewidth obtained by means of the Bloch-Bloembergern formalism show errors less than 4%. The fit gave the following parameters: averaged radius of the sample surface pits, porosity in polycrystalline sample, activation energy, and values of the conductivity. The values of the activation energy imply the existence of Fe 2ϩ cations in the sample. Additional measurements on magnetization in manganese ferrites are presented.

In this work the study of the ferromagnetic resonance (FMR) and of the electrical conductivity in the perovskite sample, Sr2FeMoO6, is presented. The sample has been manufactured by conventional ceramic method sintering in inert gas atmosphere. Electrical conductivity, of about 1000–1200 S/m, has been measured in the 125–300 K temperature range. FMR linewidths have been measured at 9.48 GHz from 125 to 300 K. A decrease of the linewidth with increasing temperature has been obtained. This behavior has been attributed to the presence of valence exchange mechanism, which takes places in samples with Fe2+ cations. In this way, FMR linewidth analysis has been revealed like a useful and clear technique in determining the cation distribution of the sample showing the presence of Fe2+ ions. This technique has also shown data about the microstructure of the sintered polycrystalline sample finding the porosity value of the sample.