Study of physical, magnetic and transport properties of cations substituted NiCuZn based spinel ferrites

Abstract

The present research focused on the study of the physical, magnetic and transport properties of various Ni0.37-xCu0.10Zn0.53+xFe2O4, Ni0.27-xCu0.20Zn0.53+xFe2O4 and Ni0.27Cu0.10Zn0.63AlxFe2-xO4. Powders of all compositions have been synthesized by auto combustion method. Pellet and toroid-shaped samples prepared from each composition are sintered at different sintering temperatures (Ts) in air for 5 hours. The structural and surface morphology were studied by X-ray diffraction (XRD) and Scanning Electron microscopy, respectively. The magnetic properties were investigated by complex initial permeability (frequency and temperature dependent), dynamic B-H loop and DC magnetization measurements. The transport properties were studied by dielectric, impedance, modulus spectroscopy and ac conductivity measurements. The complex dielectric constant was measured as a function of frequency for all compositions. Impedance studies were performed to separate the grain and grain boundary resistance whereas dynamical aspect of conductivity known from modulus analysis. To know the dynamical aspect of conduction mechanism frequency dependent conductivity has been carried out. The XRD analyses revealed that all compositions exhibit single phase and formed cubic spinel structure. The lattice constant increased from 8.405 to 8.421 Å and 8.413 to 8.429 Å with the increase in Zn content for Ni0.37-xCu0.10Zn0.53+xFe2O4 and Ni0.27-xCu0.20Zn0.53+xFe2O4, respectively whereas it decreased from 8.420 to 8.409 Å with the increase in Al content for Ni0.27Cu0.10Zn0.63AlxFe2-xO4. This is due to the substitution of larger Zn2+ (0.73 Å) compared to that of Ni2+ (0.69 Å) and Cu2+ (0.72 Å) , and substitution of smaller Al3+ (0.535 Å) compared to that of Fe3+ (0.645 Å). Both X-ray (𝜌𝑋) and bulk density (𝜌𝐵) decreased with the increase in Zn content for Ni0.37-xCu0.10Zn0.53+xFe2O4 and Ni0.27-xCu0.20Zn0.53+xFe2O4 whereas it decreased with the increase in Al content for Ni0.27Cu0.10Zn0.63AlxFe2-xO4. The 𝜌𝐵 increases up to optimum Ts due to uniform grain growth and thereafter it is decreased due to trapped pores inside the grain. Saturation magnetization decreased with the increase in Zn content for Ni0.37-xCu0.10Zn0.53+xFe2O4 and Ni0.27-xCu0.20Zn0.53+xFe2O4 whereas it initially increased with the increase in Al content up to x = 0.02 in case of Ni0.27Cu0.10Zn0.63AlxFe2-xO4. The magnetic moments followed the similar behavior. The dynamic B–H loop measurement confirms that all samples were in ferrimagnetic state at room temperature. The Bmax, Br and Hc decreased with increasing Zn content. These hysteresis parameters also showed Ts and composition dependent behavior. The variations of observed Hc are related to the microstructural evolution of the samples. The core losses (PL) decreased with increasing both Zn and Al content because of increasing Dm, / i  and decreasing crystalline anisotropy. The / i  increased with the increase in Zn content in Ni0.37-xCu0.10Zn0.53+xFe2O4 and Ni0.27-xCu0.20Zn0.53+xFe2O4 throughout the series except for x = 0.15 for the later series. The / i  increased with increasing Ts up to 1200 oC and above that / i  decreased whereas in case of Ni0.27Cu0.10Zn0.63AlxFe2-xO4; / i  increased with increasing Al content up to x = 0.02 sintered at 1100 and 1150 oC, but for higher Ts the / i  gradually decreases. At higher Ts / i  decreased due to the decrease in 𝜌𝐵 . The dielectric constant (') decreases with increasing frequency. Modulus study indicates that frequency range for mobile charge carriers over long distances increases with Zn content whereas decreases with Al content. The ac conductivity (ac) obeys the Jonscher’s universal power law. The ' and ac increase with increasing Zn content in Ni0.37-xCu0.10Zn0.53+xFe2O4 and Ni0.27-xCu0.20Zn0.53+xFe2O4 and decreases with Al in Ni0.27Cu0.10Zn0.63AlxFe2-xO4 whereas the variation of grain and grain boundary resistance show the opposite trend for Zn and Al content compositions.