Sol–gel auto combustion synthesis of CoFe2O4/1-methyl-2-pyrrolidone nanocomposite: Its magnetic characterization

A magnetic nanocomposite was generated by the sol–gel auto-combustion method in the presence of 1-methyl-2-pyrrolidone, a functional solvent. The temperature-dependent magnetic properties of the CoFe2O4 nanoparticles have been extensively studied in the temperature range of 10–400 K and magnetic fields up to 80 kOe. Zero field cooled (ZFC) and field cooled (FC) curves indicate that the blocking temperature (TB) of the CoFe2O4 nanoparticles is above 400 K. It was found from M–H curves that the low temperature saturation magnetization values are higher than bulk value of CoFe2O4. The saturation magnetization (Ms), remanence magnetization (Mr), reduced remanent magnetization (Mr/Ms) and coercive field (Hc) values decrease with increasing temperature. The Mr/Ms value of 0.75 at 10 K indicates that the CoFe2O4 nanoparticles used in this work have, as expected, cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model. T1/2 dependence of the coercive field was observed in the temperature range of 10–400 K according to Knellerʹs law. The extrapolated TB and the zero-temperature coercive field values calculated according to Knellerʹs law are almost 427 K and 13.2 kOe, respectively. The room temperature Hc value is higher than that of the previously reported room temperature bulk values. The effective magnetic anisotropy constant (Keff) was calculated as about 0.23×106 erg/cm3 which is lower than that of the bulk value obtained due to disordered surface spins.