A detailed study of permeability spectra of polycrystalline pure and Aland Gd-Substituted garnets has been carried out for different values of grain diameter and magnetisation. The spectra are of three types—resonance, relaxed and mixed. It has been shown that the resonance spectra occur when the closure demains are absent and the domain wall is anchored at the grain boundary. The relaxed spectrum is found for domains having closure flux while the mixed spectrum is an indication of simulataneous presence of grains with and without closure domains.

The wave-vector dependence of the spin-wave line-width in yttrium iron garnets has been studied for samples of grain diameter varying from 1·2µm to 12µm. An expression for the spin-wave line-width as a function of wave-vector and grain diameter has been obtained, which agrees satisfactorily with experiment.

A new hexaferrite composition, BaCo_xSi_x+yFe_12−2x−yO₁₉ (x=0·90;y=0·05), in fine (∼μ size) powder form, is prepared. Ferrite paint formulations are made by dispersing this powder in different weight proportions in an epoxy resin. X-band (8–12 GHz) microwave absorption behaviour of the paint coatings of different thicknesses is studied. Remarkably high value, ≥10 dB, of signal absorption at 9·5 GHz is observed for a coating thickness of 0·60 mm with a ferrite fill factor of 57 wt%.

Optical, mechanical and structural behaviors have been studied for titania-doped Bi₂V_1−𝑥Ti_𝑥O$_{5.5−\delta}$ which are used as electrolytes for intermediate temperature fuel cells. Parameters like band gap ($E_{g}$), Urbach energy ($E_{u}$), refractive index, hardness (𝐻) and fracture strength (𝐾) have been calculated as a function of dopant concentration, i.e. 0.05 ≤ 𝑥 ≤ 0.2. Furthermore, analysis of transmission electron microscopy (TEM) images for all the oxides was conducted along with line spectra of planes. Results are discussed in light of correlation of these optical and mechanical parameters to their structural properties. Band gap has also been correlated to the conductivity of these oxides. Good correlation has been obtained between them.

The Raman and infrared phonons in the tetragonal structure of double-perovskite Ba$_2$MgTeO$_6$ with space group I4/m have been studied using a short-range force constant model. This study used six stretching and two bending force constants to calculate zone centre phonons theoretically using the normal coordinate analysis. Some optical vibrational modes have been reported for the first time for Ba$_2$MgTeO$_6$ compounds in the I4/m phase using Wilson’s GF-Matrix method. The rest of the phonon modes calculated in this work have been compared with the available experimentally observed frequencies in the literature. The significance of interatomic force constant in the calculated Raman and infrared phonons has also been investigated in the potential energy distributions for the double-perovskite compound Ba$_2$MgTeO$_6$.