The Influence of Stoichiometry on the Index of Refraction of Cobalt Ferrite Samples at Terahertz Frequencies
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The Influence of Stoichiometry on the Index of Refraction of Cobalt Ferrite Samples at Terahertz Frequencies Alan F. N. Boss1, Antonio C. C. Migliano1,2 and Ingrid Wilke3 1 Instituto Tecnológico de Aeronáutica, São José dos Campos, SP, 12228-900 Brazil 2 Instituto de Estudos Avançados, São José dos Campos, SP, 12228-001 Brazil 3 Rensselear Polytechnic Institute, Troy, NY, 12180 USA ABSTRACT We report an experimental study on the terahertz frequency dielectric properties of manganese cobalt ferrites (MnxCo1-xFe2O4) and nickel cobalt ferrites (NixCo1-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. MnxCo1-xFe2O4 and NixCo1-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 Mn0.3Co0.7Fe2O4. This difference may be correlated to a secondary phase formed in this sample.
INTRODUCTION Ferrites are ferrimagnetic materials that play an important role in devices that operate at microwave frequencies. They can be applied e.g. in filters, absorbers, and metamaterials. Their magnetization arrives from the incomplete cancellation of the spin moments, as illustrated in figure 1 for the ferrite prototype named magnetite (Fe3O4) [1]-[2]. To advance microwave ferrite device technology to the terahertz frequency band, it is crucial to characterize ferrites at terahertz frequencies and understand their behavior. Recently, it has been proposed that ferrites have the potential to be used in the fabrication of THz wave devices and THz wave metamaterials [3]. To the best of our knowledge, no major studies of the THz frequency dielectric properties of ferrites have been performed to date. We started addressing this gap in knowledge by measuring the electric properties of nickel cobalt (NiCo) [4] and manganese cobalt (MnCo) [5] ferrites in the technologically relevant 0.2 THz to 1 THz frequency range. We believe that these ferrites may find further applications on tunable THz devices, such as circulators [6], waveguides [7] and metamaterials [8]-[9].
Downloaded from https:/www.cambridge.org/core. Monash University, on 23 May 2017 at 17:27:01, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2017.355
Figure 1. Illustration of the Fe ion arrangement in a ferrite prototype (Fe3O4). The Fe ions are represented by arrows accordantly to their spins. The ratio of Fe2+ to Fe3+ is 1:2
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