Abstract
Nickel ferrite (NiFe~2~O~4~) was synthesized by the micelles mixing method, using lyophilized coconut oil. The method leads to the formation of ferrite nanoparticles. Nickel ferrite was prepared in coconut oil suspension and annealed during 4 h, at 400, 600, 800, 1000, and 1200°C. The X‐ray diffraction (XRD) was applied to investigate the nanoparticle size dependence on the annealing temperature. Complex permittivity measurements were carried out in cavity resonators at 5.0 and 9.0 GHz, using the small perturbation theory. The main result is that the real part of the permittivity decreases with increasing annealing temperatures (3.6–2.4), while the imaginary part of the permittivity varies only for the lowest annealing temperatures, remaining low for the other samples (about 10^−3^). The X‐ray diffractograms indicates that the nanoparticle size increase with annealing temperature, allowed the correlation between the nanoparticle size and the observed microwave dielectric response. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1341–1343, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22402