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

Nanoparticles of Ni 0.5 Co 0.2 Zn 0.3 Fe 2 O 4 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 , remanent magnetization and coercivity increased with an increase in temperature from 300 to 50 K.