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Ferrite nanoparticles are in the last years a matter of strong interest due to the fact that nanoscale materials possess size-dependent optical, electronic, magnetic, thermal, mechanical, and chemical properties that are comparable to or superior to those of bulk material counterparts, as well as its potential applications in sensors or microwave devices. Nickel ferrites, which are well-known technological materials in various electronic devices, were prepared in the form of nanoparticles by a modified sol-gel technique employing coconut oil, and then annealed at different temperatures in the 400° C-1200 ° C range. This route of preparation has been revealed to be one efficient and cheap technique to obain high-quality nickel ferrite nanosized powder. Sample particle sizes obtained with X-ray diffraction data and Scherrer's formula lie in 13-138 nm, with increased size with annealing temperature. Magnetic field-induced microwave absorption in nanoscale ferrites is a recent an active area of research, in order to characterize and explore potential novel applications. In the present work, microwave magnetoabsorption data of the annealed nickel ferrite nanoparticles are presented. These data have been obtained with a system developped in our laboratory, based on a network analyzer that operates in the frequency range 0-8.5 GHz. We can observe a resonance peak with applied fields of up to 400 mT. The results are interpreted on the basis of ferromagnetic resonance theory. [ABSTRACT FROM AUTHOR]

Transmittance measurements on diluted barium ferrite materials in broadband millimeter-wave frequency range have been performed. The measurements have been done using free-space quasi-optical spectrometer in transverse magnetic field up to 7.5 kOe. A set of backward wave oscillators have been used as sources of high power coherent radiation tunable in 34–120 GHz frequency region. A magnetooptical approach has been employed for the separation of dielectric and magnetic effects in ferrites and simultaneous determination of complex dielectric permittivity and magnetic permeability of materials. It has been shown that a variation in the chemical composition of ferrites leads to a change in the magnetic properties and absorption of materials in the millimeter waves. [ABSTRACT FROM AUTHOR]