Infrared Properties of NiO-SrTiO$_{3}$ Composites

Magnetic-dielectric composites with overlapping magnetic- and electric-dipole resonances are promising candidates in the search for artificial systems with negative refractive index [1]. Here we report on the fabrication and infrared characterization of NiO-SrTiO$_{3 }$~ceramics. Transmission and reflection data were obtained in the 10-700 cm$^{-1}$ range using both a THz time-domain and a FTIR spectrometer. The spectra show features associated with the bulk antiferromagnetic resonance of NiO and the soft mode of SrTiO$_{3}$, as well as new collective modes of the aggregate. The results are in qualitative agreement with effective medium theories. \newline [1] S. D. Kirby, M. Lee, R. B. van Dover, J. Phys. D \textbf{40,} 1161 (2007)