Dielectric properties of magnetic grains in CoFe1.95Ho0.05O4 spinel ferrite

Abstract

CoFe1.95Ho0.05O4 spinel ferrite has been prepared by mechanical alloying and subsequent annealing at temperatures (TAN) in the range 800–1200°C. As an effect of annealing temperature, the average grain size of the material has increased from 40 to 90nm and magnetically transformed from single domain/pseudo-single domain (40–64nm) to multi-domain state (67–90nm) for TAN>1050°C. Dielectric properties of the nano-grained CoFe1.95Ho0.05O4 ferrite have suggested a correlation with magnetic domain transformation. The dielectric constant of the material is the lowest for the grains in pseudo-single domain state (59nm). The material showed non-Debye type dielectric relaxation with activation energy 0.47–0.58eV, along with lowest value of activation energy due to electrical conduction inside grains. The dielectric contributions of grains and grain boundaries have been precisely separated using complex modulus formalism and various scaling plots. Results of the dielectric parameters of the samples (dielectric constant: 20–100 and dielectric loss: 0.11–0.4) seems to be interesting for microelectronic applications of ferrite materials.