Sol-gel auto combustion synthesis of CoFe_2O_4/1-methyl-2-pyrrolidone nanocomposite: Its magnetic characterization

摘要

A magnetic nanocomposite was generated by the sol-gel auto-combustion method in the presence of l-methyl-2-pyrrolidone, a functional solvent. The temperature-dependent magnetic properties of the CoFe_2O_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_2O_4 nanoparticles is above 400 K. It was found from M-H curves that the low tempera ture saturation magnetization values are higher than bulk value of CoFe_2O_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_2O_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 x 106 erg/cm3 which is lower than that of the bulk value obtained due to disordered surface spins.