Optimizing superparamagnetic CoFe₂O₄ nanoparticles: bridging theoretical models and experimental observations

This study investigates the synthesis and characterization of CoFe2O4 nanoparticles with forced hydrolysis method. Transmission Electron Microscopy (TEM) analysis revealed well-crystallized particles with an average diameter of 6 nm. The magnetic properties were extensively characterized through isothermal magnetic hysteresis measurements (±60kOe) across a temperature range of 3-400 K, revealing strong temperature-dependent behavior with saturation magnetization decreasing from 75 emu/g to 48 emu/g. The squareness ratio analysis (0.47-0.55) indicated a unique mixed magnetic anisotropy system combining both cubic and uniaxial characteristics. ZFC and FC magnetization measurements under 50, 100, and 300 Oe applied fields demonstrated field-dependent blocking temperatures ranging from 215 K to 226 K. The first-order magneto-crystalline anisotropy constant (K1) showed temperature dependence with a zero-temperature value of 7.95 × 106 erg/cm3. A notable discrepancy between theoretically (2.5 nm) and experimentally (6 nm) calculated average size suggested complex magnetic interactions at the nanoscale. High-temperature magnetic behavior revealed unusual characteristics in the superparamagnetic regime, with Curie-Weiss temperatures significantly lower than typical ferrimagnetic-paramagnetic transitions. These findings provide crucial insights into the fundamental magnetic properties of CoFe2O4 and its potential applications in advanced magnetic technologies.