Sol–gel auto combustion synthesis of CoFe 2 O 4 /1-methyl-2-pyrrolidone nanocomposite: Its magnetic characterization

Abstract 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 CoFe 2 O 4 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 ( T B ) of the CoFe 2 O 4 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 CoFe 2 O 4 . The saturation magnetization ( M s ), remanence magnetization ( M r ), reduced remanent magnetization ( M r / M s ) and coercive field ( H c ) values decrease with increasing temperature. The M r / M s value of 0.75 at 10 K indicates that the CoFe 2 O 4 nanoparticles used in this work have, as expected, cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model. T 1/2 dependence of the coercive field was observed in the temperature range of 10–400 K according to Kneller's law. The extrapolated T B and the zero-temperature coercive field values calculated according to Kneller's law are almost 427 K and 13.2 kOe, respectively. The room temperature H c value is higher than that of the previously reported room temperature bulk values. The effective magnetic anisotropy constant ( K eff ) was calculated as about 0.23×10 6 erg/cm 3 which is lower than that of the bulk value obtained due to disordered surface spins.