The Impacts of Various Metal Cations on Structural, Dielectric and Magnetic Properties of Nanocrystalline Nickel and Magnesium Ferrites

Abstract

A systematic investigation on the structural, spectral, magnetic and dielectric properties of transition metals doped magnesium and nickel based spinel ferrites by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM) and dielectric measurements was carried out. These spinel ferrites were fabricated by the micro-emulsion technique. The analysis of XRD patterns confirmed the single phase spinel structure of these spinel ferrites. The crystallite size was calculated by Scherrer’s formula. The crystallite sizes lie in the range of 10 - 45 nm. The lattice constant of the prepared ferrites exhibited a good agreement with the earlier reports for similar types of ferrites synthesized by various methods. The spectral studies elucidated the characteristic features of spinel ferrites. The FTIR studies confirmed the formation of the metal oxide bonds in these ferrites. The saturation magnetization (Ms) increased from 9.84 to 24.99 emu/g up to x = 0.2, y = 0.4 and then decreased. The coercivity (Hc) increased continuously from 94 to 153 Oe with the increase in dopants concentration in MgxNi1-xCoyFe2-2yO4. In Ni0.5Sn0.5CoxMnxFe2-xO4 saturation magnetization (Ms) gradually increased from 20.48 emu/g to 47 emu/g with an increase in the value of x. However, coercivity increased from 152.67 Oe to 463.35 Oe with x = 0.0 to 0.4 respectively. Thereafter it decreased from 371.44 Oe to 158.91 Oe for x = 0.6 - 0.8 respectively. The coercivity decreased from 40.6 to 13.09 emu/g up to x = 0.8 with ups and downs in between x = 0.0 to x = 0.8 for NiZrxCoxFe2-2xO4. These results showed that both Co2+ ions occupy mainly the B-site while Fe3+ ions were equally distributed among A- and B-sites. The redistribution of the cations between A and B sites caused an increase in saturation magnetization. The magnetic parameters have been explained on the basis of exchange energy, magnetocrystalline anisotropy and spin canting which is the outcome of nano-regime. The increase in the tendency of saturation magnetization was consistent with the enhancement of crystallinity. The crystallite size of all the synthesized ferrites was small enough to obtain considerable signal to noise ratio for their potential use in the recording media. The dielectric properties have been explained on the basis of Debye-type relaxation phenomenon in accordance with Koop’s phenomenological theory. The frequency dependent dielectric parameters such as dielectric permittivity (ε) and ac conductivity (σAC) have been studied in the frequency range 1MHz to 3 GHz. These parameters indicated that the dielectric dispersion curve for all samples showed usual dielectric dispersion confirming the thermally activated xx relaxation typical for Debye-like relaxation referring to it as the Maxwell-Wagner relaxation for the interfacial polarization of homogeneous double layer structure. The optimized dielectric and magnetic parameters of Mg0.6Ni0.4Co0.4Fe1.6O4 ferrite suggested its possible use in microwave devices and recording media applications. The real and imaginary parts of dielectric constant and dielectric loss exhibit peaking behavior. The dielectric parameters were found to decrease with the increased calcium and nickel concentration. Further the peaking behavior was observed beyond 1.5 GHz. The frequency dependent dielectric properties of all the samples have been explained qualitatively on the basis of the Maxwell-Wagner two-layer model according to Koop's phenomenological theory. The enhanced magnetic parameters and reduced dielectric properties make the synthesized ferrites suitable for switching and high frequency applications, respectively. The frequency dependence of dielectric constant has been explained on the basis of hopping of both electrons and holes. The dielectric constant indicated that present nanoferrites have great potential for microwave applications.