Effects of Al3+ Substitution on Structural and Magnetic Behavior of CoFe₂O₄ Ferrite Nanomaterials.

Qing Lin,Yun He,Jinpei Lin,Zeping Guo,Jianmei Xu,Fang Yang

doi:10.3390/nano8100750

Abstract

A sol-gel autocombustion method was used to synthesize Al3+ ion-substituted cobalt ferrite CoAlxFe2−xO4 (x = 0–1.5). According to X-ray diffraction analysis (XRD), cobalt ferrite was in a single cubic phase after being calcined at 1000 °C for 3 h. Moreover, the lattice constant decreased with increase in aluminum substituents. When the sample was analyzed by Scanning Electron Microscopy (SEM), we found that uniformly sized, well-crystallized grains were distributed in the sample. Furthermore, we confirmed that Al3+ ion-substituted cobalt ferrite underwent a transition from ferrimagnetic to superparamagnetic behavior; the superparamagnetic behavior was completely correlated with the increase in Al3+ ion concentration at room temperature. All these findings were observed in Mössbauer spectra. For the cobalt ferrite CoAlxFe2−xO4, the coercivity and saturation magnetization decrease with an increase in aluminum content. When the annealing temperature of CoAl0.1Fe1.9O4 was steadily increased, the coercivity and saturation magnetization initially increased and then decreased.

Highlights

Ferrite CoAlxFe2−xO4 (x = 0–1.5) materials were synthesized with a sol-gel autocombustion process
The X-ray diffraction analysis (XRD) spectra of CoAl0.1Fe1.9O4 samples were obtained after sintering them at different temperatures; these samples were prepared with a sol-gel autocombustion method, so they had good crystallinity
The Mössbauer spectra reveal that with an increase in aluminum concentration, CoAlxFe2−xO4 samples undergo a transition from ferrimagnetic behavior to superparamagnetic behavior

Summary

Introduction

Cobalt ferrite is a hard ferromagnetic material, and its characteristic properties are as follows: moderate saturation magnetization (80 emu/g), high coercivity (5000 Oe), high Curie temperature TC (520 ◦C), large anisotropy constant (2.65 × 105– 5.1 × 105 J/m3) [1,2]. Cobalt ferrite substituted nonmagnetic Al3+ ions; such material has low magnetic coercivity and large resistivity. In AlxCoFe2−xO4 ferrite powders, saturation magnetization and coercive force decrease with increasing concentration of Al. In a study conducted by Kumar et al [7], it was found that crystallite size of cobalt ferrite increased when they were doped with Al3+ ions. The aim of this study was to determine the variation in the magnetic performance of cobalt ferrite powders, which were partially doped with nonmagnetic aluminum cations

Objectives

Results

Conclusion