Sol–Gel Route for the Synthesis of CoFe<sub>2–<i>x</i></sub>Er<sub><i>x</i></sub>O<sub>4</sub> Nanocrystalline Ferrites and the Investigation of Structural and Magnetic Properties for Magnetic Device Applications
Minhajul Islam, M.K.R. Khan, Alok Kumar, Mahbubur Rahman, Md. Abdullah Al Mamun, Rimi Rashid, Md. Mahbubul Haque, M.S.I. Sarker
Abstract
High Resolution Image Download MS PowerPoint Slide This study reports the formation of Er-doped nanocrystalline cobalt ferrite with the formula CoFe 2– x Er x O 4 (0.0 ≤ x ≤ 0.10) from nontoxic metal precursors Co(NO 3 ) 2 ·6H 2 O, Fe(NO 3 ) 3 ·9H 2 O, and Er(NO 3 ) 3 ·5H 2 O through an easy and economical sol–gel route in which citric acid is served as the chelating agent. The as-prepared powder was annealed at 700 °C for 3 h in ambient air to get the required spinel structure. The annealed samples were subjected to structural and magnetic characterization. The X-ray diffraction (XRD) data of the samples confirmed the cubic spinel structure formation. The average crystallite size evaluated from XRD data increased from 21 to 34 nm with the substitution of Er due to the larger atomic size of Er 3+ than Fe 3+ . Moreover, the crystallite size obtained from XRD data are well matched with the particle size measured from transmission electron microscopy images. The lattice parameters obtained from XRD data agree well with the values estimated from theoretical cation distribution and Rietveld refinement calculation. The hysteresis curve exhibits the particles are soft ferromagnetic and the coercivity increased from 54.7 to 76.6 kA/m with maximum saturation magnetization, M s = 61 emug –1 for 0.10 Er content. The squareness ratios were found to be less than 0.5, which indicates the single-domain nature of our particles. The blocking temperature measured from field cooled-zero field cooled curves is T B > 350 K for all the samples, which is much higher than the room temperature (300 K). The enhancement of saturation magnetization and coercivity has been explained based on the crystallite size, anisotropy constant, and cation distribution. Thus, the structural and magnetic properties of CoFe 2 O 4 nanoparticles (NPs) can be tuned by Er incorporation and these NPs can be applied in different soft magnetic devices.