Single phase metamaterial behavior in [formula omitted] and [formula omitted] doped cobalt ferrites

Abstract

This paper reports the characteristic properties of CoFe2O4(CFO), Co0.98Ag0.02Fe2O4(CAFO), and Co0.98Ti0.02Fe2O4(CTFO) spinel ferrites of Fd3‾m space group and grain size in the range of 160 – 170 nm. Fourier transform infrared spectra of these samples have revealed the metal-oxygen bands in the range of 448– 542 cm−1. Raman spectra have shown six distinct peaks corresponding to the mixed spinel structure, which have been used to calculate the cation distribution of the samples. The magnetic measurement at room temperature shows that after the doping of Ti4+ ions, the saturation magnetization increases from 47.70 to 66.68 emu/g, and coercivity decreases from 1.84 to 1.61 kOe, making the sample magnetically softer. The law of approach to saturation magnetization has been used to estimate the value of magneto crystalline anisotropy constant. The dielectric behavior of the samples has been thoroughly studied in this paper. The dielectric constant is positive below 300 °C; its value is comparable for CFO and CAFO samples but higher for CTFO. Above this temperature, the samples show an uncommon behavior of negative dielectric constant corresponding to the single phase metamaterial state and its value increases as temperature rises. This behavior can be interpreted with the help of Drude model of plasmonic resonance. The Nyquist plots change their properties from RC to RL type in this region. Such single phase metamaterials with negative dielectric constant could be useful for high temperature microwave applications.