XPS and Magnetic Properties of CoFe₂O₄ Nanoparticles Synthesized by a Polyacrylamide Gel Route

Abstract

Cobalt ferrite CoFe₂O₄ nanoparticles were prepared via a polyacrylamide gel route and were characterized by XRD, SEM, XPS and VSM. It is demonstrated that the sample (designated S1) prepared without using the cross-linking agent bis-acrylamide has an average grain size of 45 nm, while the sample (designated S2) prepared by introducing an amount of bis-acrylamide which is about 1/5 times the amount of acrylamide has an average grain size of 23 nm. The two kinds of particles are shaped like spheres. The cation distribution is determined, from Co 2p_3/2 and Fe 2p_3/2 XPS spectra, to be (Co_0.4Fe_0.6)[Co_0.6Fe_1.4]O₄ for both the samples, where (Co_0.4Fe_0.6) and [Co_0.6Fe_1.4] represent cations in the tetrahedral and octahedral sites, respectively. Magnetic measurement reveals a saturation magnetization of 67.3 A·m²·kg⁻¹ for sample S1 and 62.3 A·m²·kg⁻¹ for sample S2, but a similar coercivity of about 87.5 kA·m⁻¹ for both the samples.