The Influence of Stoichiometry on the Index of Refraction of Cobalt Ferrite Samples at Terahertz Frequencies

Abstract

We report an experimental study on the terahertz frequency dielectric properties of manganese cobalt ferrites (Mn_xCo_1−xFe₂O₄) and nickel cobalt ferrites (Ni_xCo_1-xFe₂O₄) with three different stoichiometry each, x=0.3, x=0.5 and 0.7. Particularly, we present a comparison and discussion of the terahertz frequency indices of refraction of these two ferrites compositions. Mn_xCo_1−xFe₂O₄ and Ni_xCo_1-xFe₂O₄ pellets with different Mn/Co and Ni/Co ratios (x=0.3, x=0.5 and x=0.7) were prepared by state-of-the-art ceramic processing. The morphology and chemical homogeneity of these ferrites were characterized by energy dispersive x-ray spectroscopy. We observed that the indexes of refraction for manganese cobalt ferrites are 3.22, 3.71 and 3.67 for ratios of 0.3, 0.5 and 0.7, respectively. In the case of nickel cobalt ferrite, the indexes of refraction are 3.53, 3.57 and 3.47 for ratios of 0.3, 0.5 and 0.7 respectively. We notice a substantial difference in the index of refraction for the Mn_0.3Co_0.7Fe₂O₄. This difference may be correlated to a secondary phase formed in this sample.