Effects of co-substitution of Al3+ and Cr3+ on structural and magnetic properties of nano-crystalline CoFe2O4 synthesized by the sucrose technique

Abstract

Al–Cr substituted CoFe2O4 nano spinels (CoAlxCrxFe2−2xO4 where x = 0.1 to 0.6) were successfully prepared for the first time via sucrose sol–gel auto-combustion technique. The structural parameters as well as magnetic and electrical properties of the prepared ferrites have been investigated. X-ray diffraction (XRD) confirmed single-phase formation and showed a decrease in the calculated values of lattice parameters by substitution attributed to the difference in the ionic radii. Based on the obtained structural parameters, an appropriate cation distribution was proposed and discussed. In this distribution, most of Al3+ and Cr3+ ions preferred octahedral sites occupation however, small amount of Al3+ seek the tetrahedral sites. Accordingly, the magnetic characterization via vibrating sample magnetometer (VSM) measurements revealed a decrease in the saturation magnetization (Ms) by successive substitution from 57.9 to 4.7 emu/g, indicating the incorporation of non-magnetic Al3+ and anti-ferromagnetic Cr3+ ions in the octahedral sites instead of Fe3+ ions. The much lower magnetization values obtained than that prepared by other methods could be attributed to the present lower sizes. The coercivity measurements indicated soft ferrimagnetic properties favoring their uses as high frequency transformers. Ac-conductivity as well as dielectric properties, as a function of frequency and temperature, indicated semiconducting behavior with decreasing trend by Al–Cr substitution due to decreasing in the Fe3+-Fe2+ hopping probability in octahedral sites. The obtained results suggest the using of the present materials in electronic inductors, electromagnets and transformers and microwave devices.

Keywords

• Al–Cr substitution
• Cation distribution
• Auto-combustion
• Magnetization
• Conductivity