Magnetic and RF-electromagnetic absorbing study of aluminum doped nickel ferrites prepared by two techniques

Abstract

Pure phase aluminum doped nickel ferrite nanoparticles [NiAlxFe2−xO4] with x = 0.0, 0.25 and 0.5 have been investigated for magnetic and electromagnetic absorbing properties in S band and influence of Al3+ ions has been studied. Nickel aluminum ferrites have been synthesized by co-precipitation and sol–gel auto combustion routes. Magneto-dielectric properties were measured in terms of complex permeability (μ*) and complex permittivity (ϵ*) at 300 K in the frequency range of 1 MHz to 3 GHz using RF material/impedance analyzer. Dielectric permittivity (ϵ′ and ϵ″) has been observed to decrease with the increase in applied frequency and concentration of aluminum ions (x = 0.0–0.5). Magnetic permeability (μ′ and μ″) has been found to decrease with the increase in aluminum ions concentration. Electromagnetic absorbing properties were studied for all the samples by calculating the reflection losses (RL) in the frequency range of 1 MHz–3 GHz using the permittivity and permeability measurements in accordance with the transmission line theory. RL (dB) values lie in the range of −42 dB to −57 dB. RL values (> −10 dB) confirm more than 90% absorption of electromagnetic waves incident normal to the material surface. Aluminum doping has increased the RL values from −45 dB to −57 dB along with the shift of RL dip towards the higher frequency side for the samples prepared by sol–gel auto combustion technique. Magnetic properties have been studied by vibrating samples magnetometer (VSM) at room temperature and a decrease in magnetic properties has been observed due to increase in x from 0.0–0.5.