FTIR and Electrical Study of Dysprosium Doped Cobalt Ferrite Nanoparticles

We have studied the role of Dy3+ doping on the XRD, TEM, FTIR, and dielectric and electrical properties of CoFe2O4 at room temperature. Cubic spinel phase of CoFe2？xDyxO4 ( = 0.00, 0.05, 0.10, and 0.15) was synthesized by using different sintering temperatures (300, 500, 700, and 900°C). The two absorption bands ν1 and ν2 are observed in Fourier transform infrared spectroscopy (FTIR) spectra corresponding to the tetrahedral and octahedral sites, which show signature of spinel structure of the sample. For the sample sintered at 300°C, the dielectric constant is almost unchanged with the frequency at the particular concentrations of = 0.00 and 0.05. Similar result is obtained for the sample sintered at 500°C ( = 0.10, 0.15), 700°C ( = 0.05, 0.10, and 0.15), and 900°C ( = 0.05, 0.10). An increase in the dielectric constant was observed for the undoped cobalt ferrite sintered at 500, 700, and 900°C. The values of electrical resistivity of the materials vary from ~105 to 109？Ω-cm. 1. Introduction Spinel ferrites have general formula MO: Fe2O3 where M is Zn2+, Ni+2, Co+2, and so forth. It constitutes an important class of magnetic materials having several technological applications like spintronics, magnetic diagnostic, magnetic drug delivery, storage devices, electrical generators, microwave devices, and so forth [1]. Nanoferrites exhibit unusual electrical, magnetic, and optical properties which are sensitive to their structure, method of synthesis, particle size, and type of dopant ions. These materials crystallize into a cubic closed-packed structure of oxygen ions. The cations occupy two types of interstitial sites known as tetrahedral (A) site and octahedral (B) site. The site occupancy is often depicted by the chemical formula ( )[ ] , ？where the parentheses and square brackets denote A and B sites, respectively, M represents a divalent cation, and is inversion parameter [2]. Among spinel ferrites, CoFe2O4 is an interesting magnetic material due to its high coercivity (~5400？Oe) and moderate saturation magnetization (~80？emu/g) as well as remarkable chemical stability and mechanical hardness, which make it a good candidate for the recording media [3, 4]. The coexistence of spontaneous polarization and magnetization in CoFe2O4 based composite and core shell nanoparticles is of great importance [5]. However, synthesising composites and core-shell particles is a complicated task rather than synthesizing single phase materials. Doping of Zn in the cobalt ferrite matrix leads to the increase of dielectric constant, whereas nickel substitution leads to the