Engineering superparamagnetic quantum-sized Ca <sup>2+</sup> -doped CoFe₂O₄ nanomaterials
Anchal, Sarita Sarita, Yashpal Choudhary, Narendra Jakhar, P. A. Alvi, B. L. Choudhary
Abstract
This study reports the synthesis of superparamagnetic CaxCo1-xFe2O4 nanoparticles (x = 0.1, 0.3, 0.5) via the sol-gel method using citric acid as a chelating agent. XRD and Rietveld refinement confirmed a cubic crystal structure (Fd-3m), with crystallite size decreasing from 5.8 to 5 nm as Ca2+ concentration increased, placing them in the quantum dot regime. Williamson-Hall analysis assessed micro-strain, while FESEM revealed predominantly spherical nanoparticles. Raman and FTIR spectra confirmed key vibrational modes and characteristic bonds. UV–Vis. spectroscopy showed a decreasing optical bandgap and increasing Urbach energy with higher Ca2+ levels, supported by PL analysis. XPS provided insight into elemental oxidation states. Magnetic measurements via VSM exhibited low remanence and coercivity, along with a squareness ratio exceeding 0.5, confirming their superparamagnetic behavior. CaxCo1−xFe2O4