Efficient hydrothermal fabrication of chromium-doped manganese ferrite nanoparticles: The impact of Cr concentration on their magnetic and structural characteristics

This study investigates the structural, morphological, textural, and magnetic properties of chromium-doped manganese ferrite (MnCr x Fe 2-x O 4 , x = 0, 0.1, 0.2, 0.3) nanoparticles synthesized via a hydrothermal method. X-ray diffraction (XRD) analysis confirmed a primary cubic spinel structure with a secondary Mn 3 O 4 impurity phase in all samples. A non-monotonic variation in the lattice parameter and crystallite size was observed, with a minimum at x = 0.2, indicating maximum lattice strain and dislocation density. Fourier-transform infrared (FTIR) spectroscopy revealed shifts in metal-oxygen bond vibrations, confirming Cr 3+ incorporation into the octahedral sites of the spinel lattice. Electron microscopy (SEM/TEM) showed that Cr-doping refined particle morphology, resulting in smaller, more uniform, spherical nanoparticles. Energy-dispersive X-ray spectroscopy (EDXS) verified successful doping but revealed a consistent excess of Cr and Mn compared to theoretical stoichiometry. BET surface area analysis demonstrated that Cr-doping significantly enhanced the specific surface area, which peaked at 602.68 m 2 /g for x = 0.3. Magnetic characterization revealed ferrimagnetic behavior at 5 K and superparamagnetism at RT. Saturation magnetization decreased with increasing Cr content due to the substitution of higher-moment Fe 3+ ions with lower-moment Cr 3+ ions. Coercivity and remanence at 5 K exhibited a maximum at the x = 0.2 composition, correlating with its minimized structural parameters. The findings demonstrate that Cr-doping effectively tailors manganese ferrite nanoparticles' structural and magnetic properties, enhancing their potential for catalysis, biomedicine, and spintronics applications.