Cobalt-Based Ferrites Characterization Using Two Different Terahertz Time-Domain Spectrometers Alan Fernando Ney Boss 1 & Hudson de Araújo Batista 2 & Ana Cristina Figueiredo de Melo Costa 2 & Antonio Carlos da Cunha Migliano 1,3 & Ingrid Wilke 4 Received: 12 March 2018 /Accepted: 23 July 2018/ # Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract We report an experimental study of the electrical properties of manganese cobalt (MnCo) and nickel cobalt (NiCo) ferrites in the terahertz (THz) frequency band. The study is motivated by the potential of MnCo, NiCo, and other magnetic ceramics for the fabrication of active and passive devices for THz wave communications. Using two different terahertz (THz) time- domain spectroscopy systems, we characterized the optical constants of cobalt ferrites doped with manganese and nickel in the technologically important 0.2–1 THz frequency band. The MnCo and NiCo ferrites investigated in our study exhibit a lower refractive index and absorption coefficient in the 0.2–1 THz frequency band than commercial strontium ferrite. We observed that using different valency ion oxide leads to a sudden change of the refractive index as a function of sample stoichiometries. Our experimental results provide evidence that microwave ferrite technology can be extended to the THz frequency band. Keywords Refractive index . Spinel ferrite . Nickel . Manganese Journal of Infrared, Millimeter, and Terahertz Waves https://doi.org/10.1007/s10762-018-0526-y * Alan Fernando Ney Boss alan.boss86@gmail.com 1 Instituto Tecnológico de Aeronáutica–Ciências e Tecnologias Espaciais, São José dos Campos, SP, Brazil 2 Centro de Ciências e Tecnologia, Universidade Federal de Campina Grande, Campina Grande, PB, Brazil 3 Departamento de Ciência e Tecnologia Aeroespacial–Divisão de Física Aplicada, Instituto de Estudos Avançados, São José dos Campos, SP, Brazil 4 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY, USA