Nickel-cobalt-zinc ferrite nanoparticles for radio-frequency/terahertz frequency-selective surface application

Nanoparticles of Ni_0.5Co_0.2Zn_0.3Fe₂O₄ were prepared using the sol-gel combustion route. The nanoparticles were characterised by x-ray diffraction to confirm single-phase formation in a cubic spinel structure. Micro- and nanostructural analyses were carried out using field emission-scanning electron microscopy and field emission-transmission electron microscopy, respectively. A planetary ball milling technique was used to grind the powder into nanoparticles; the average particle size was 64 nm. Energy-dispersive X-ray spectroscopy was used to determine the atomic composition of the sample. Radio-frequency characteristics were recorded for dielectric measurement in a frequency range of 1 Hz to 15 MHz using a broadband dielectric spectrometer. Terahertz (THz) time-domain spectroscopy was performed to study THz-optical parameters such as refractive index, dielectric constant, and conductivity at room temperature in a frequency range of 0.3−2.2 THz using an indigenously developed THz time-domain spectroscopy setup. The magnetic properties of the sample were studied using a SQUID vibrating sample magnetometer under an applied magnetic field of ±10 kOe. An examination of M-H loops revealed that the saturation magnetization $\left(M_s\right)$, remanent magnetization $\left(M_r\right)$ and coercivity $\left(H_c\right)$ increased with an increase in temperature from 300 to 50 K.