Dopant driven tunability of dielectric relaxation in MxCo(1-x)Fe2O4 (M: Zn2+, Mn2+, Ni2+) nano-ferrites

• Published in: Journal of applied physics 2017-07, Vol.122 (3)
• Main Authors: Datt, Gopal, Abhyankar, A. C.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.4990275

Nano-ferrites with tunable dielectric and magnetic properties are highly desirable in modern electronics industries. This work reports the effect of ferromagnetic (Ni), anti-ferromagnetic (Mn), and non-magnetic (Zn) substitution on cobalt-ferrites' dielectric and magnetic properties. The Rietveld analysis of XRD data and the Raman spectroscopic study reveals that all the samples are crystallized in the Fd-3m space group. The T2g Raman mode was observed to split into branches, which is due to the presence of different cations (with different vibrational frequencies) at crystallographic A and B-sites. The magnetization study shows that the MnCoFe2O4 sample has the highest saturation magnetization of 87 emu/g, which is attributed to the presence of Mn2+ cations at the B-site with a magnetic moment of 5   μ B . The dielectric permittivity of these nanoparticles (NPs) obeys the modified Debye model, which is further supported by Cole-Cole plots. The dielectric constant of MnCoFe2O4 ferrite is found to be one order higher than that of the other two ferrites. The increased bond length of the Mn2+-O2- bond along with the enhanced d-d electron transition between M n 2 + / C o 2 + ⇋ F e 3 + cations at the B-site are found to be the main contributing factors for the enhanced dielectric constant of MnCoFe2O4 ferrite. We find evidence of variable-range hopping of localized polarons in these ferrite NPs. The activation energy, hopping range, and density of states N E F , of these polarons were calculated using Motts' 1/4th law. The estimated activation energies of these polarons at 300 K were found to be 288   meV , 426   meV , and 410   meV , respectively, for the MnCoFe2O4, NiCoFe2O4, and ZnCoFe2O4 ferrite NPs, while the hopping range of these polarons were found to be 27.14 Å, 11.66 Å, and 8.17 Å, respectively. Observation of a low dielectric loss of ∼0.04, in the frequency range of 0.1–1 MHz, in these NPs makes them potential candidates for energy harvesting devices in the modern electronics industry.