Exchange bias effect in CoFe_2O_4-Cr_2O_3 nanocomposite embedded in SiO_2 matrix

摘要

A nanogranular system composed of CoFe_2O_4-Cr_2O_3 core-shell nanoparticles (embedded in SiO_2 matrix) having average particle size of 35 ± 5 nm was prepared by chemical synthesis. Structural characterizations by x-ray diffraction, Transmission Electron Microscope (TEM) show highly crystalline phase of these nanocomposites. High resolution TEM images show distorted and modified grain boundary region. CoFe_2O_4-Cr_2O_3 nanocomposites show excellent positive exchange bias effect after field cooling at 100 Oe of applied field. Both the exchange bias field and vertical shift in magnetization loop has been observed in this system below 300 K after field cooling. There is a positive loop shift of about 5 kOe along the field axis at 20 K in this system while the vertical shift is nearly 100% owing to the strong exchange bias effect. The exchange bias effect has been explained in terms of the different magnetic exchange interactions and modified grain boundary effect of CoFe_2O4-Cr_2O_3 nanocomposites. The role of spin glass like phase and surface effects of the nanocomposite on the vertical shift of the hysteresis loop and the sharp increase of exchange bias field (H_(EB)) has also been discussed.