Abstract
A polyvinylpyrrolidone (PVP)/MnFe2O4 nanocomposite was prepared by the sol-gel autocombustion method and its structural, thermal, spectroscoppic, morphological and magnetic characterizations were done by XRD, FT-IR, TGA, SEM and VSM techniques. The presence of MnFe2O4 was confirmed by XRD and the size of crystallites was estimated to be 11 +/- 3 nm. Morphology analysis by SEM revealed spherical agglomerates of 15 nm. The magnetization curves confirm a superparamagnetic behavior with a blocking temperature of 287 K. The M-r/M-s value suggests the presence of uniaxial anisotropy in MnFe2O4 nanoparticles, instead of the expected cubic anisotropy according to the Stoner-Wohlfarth model. The effective magnetic anisotropy constant K-eff has been determined to be about 1.42 x 10(6) erg/cm(3) which is significantly higher than that of the bulk MnFe2O4. This suggests a strong magnetic coupling between magnetically ordered core spins and disordered surface spins of the nanoparticles in the nanocomposite.