Magnetic and Optical Studies of NiFe2O4 Micro- and Nanoparticles

The nickel ferrite micro- and nanoparticles have been prepared via solid-state and sol-gel auto-combustion technique and its single-phase formation, cubic spinel crystal structure (space group Fd-3m), and surface morphology were confirmed by XRD, FESEM, and TEM techniques, respectively. The optical band gap was estimated from reflectance spectra using the Kubelka-Munk equation and the direct optical band gap enhances in nanoparticles (1.905 eV) than microparticles (1.75 eV) due to the quantum confinement effect. The small value of remanence magnetization (M-r) and coercive field (H-c) of nanoparticles was observed from narrow hysteresis M-H loop which recommends its superparamagnetic states near room temperature (296 K). The absence of blocking temperature for microparticles from 0 to 300 K confirms the non-existence of a single-domain region and superparamagnetic states.