Dielectric and electrical characterizations of transition metal ions-doped nanocrystalline nickel ferrites

This paper describes the room temperature dielectric and electrical response of several transition metal ions (Cr3+, Mn2+, Zn2+ and Cd2+)-doped nickel ferrite nanoparticles. The formation of pure cubic spinel phase, microstructural and magnetic properties of these three series of nanocrystalline-doped nickel ferrite samples was reported in previous papers. It is observed that hopping of electrons is the possible charge conduction mechanism for all doped nickel ferrite samples at room temperature. All the doped ferrite samples exhibited increment in ac conductivity with increasing ac field frequency. The hopping length is found to decrease with increasing dopant concentration in Zn-Cd-Ni ferrite and Cr-Ni ferrite. For Mn-doped nickel ferrite, a slight increase in hopping length is observed. All the doped nanoferrites showed good dielectric behavior below 100 Hz along with a rapid decline above 100 Hz and finally attained negligible value. The existence of two semicircles in Nyquist plots indicates that grains and grains boundaries contribute more in dielectric responses.