NiFe2O4 nano-hollow spheres with improved magnetic and dielectric properties

From the detail morphology dependent studies, nano-hollow spheres (NHS) of NiFe2O4 (NFO) are found to exhibit better magnetic and dielectric properties compared to their nanoparticles and bulk counterparts. Prepared by solvothermal method, these NHS with diameter of ∼228 nm and much lower tap density of ∼3.91 g/cc, show excellent magnetic properties with MS and HC, 63.5 emu/g and 122 Oe respectively. Variation of dielectric properties such as permittivity (ε), dielectric loss (tanδ) and ac conductivity (σac) of these NHS with frequency and temperature is explained on the basis of Maxwell-Wagner two layer model for space charge and hopping of charges from Fe3+ to Fe2+ as well as Ni2+ to Ni3+ ions at B (octahedral)-sites. The complex impedance spectroscopy study indicates the presence of grain and grain boundary effects in NHS and the conduction mechanism is explained by Jonscher's power law. A comparatively low value of the activation energy (E = 0.325 eV) is found for these NHS. High value of magnetic and dielectric properties of NFO NHS enhance their potential applications for microwave devices in the form of isolators, circulators etc.