Decrease of superparamagnetic fraction at room temperature in ultrafine CoFe2O4 particles by Ag doping
R. Shukla;R. S. Ningthoujam;S. S. Umare;S. J. Sharma;Sajith Kurian;R. K. Vatsa;A. K. Tyagi;N. S. Gajbhiye;
Co1 − x Ag x Fe2O4 nanoparticles have been prepared by the combustion route. The average crystallite sizes for compositions with x = 0 and 0.2 are found to be 36 and 33 nm respectively from the XRD line broadening. Compared to the pure CoFe2O4, Ag-doping reduces the intrinsic magnetization values (M, M r), but enhances coercivity (H c). Mössbauer spectra show two sextets, indicating occupancies of tetrahedral and octahedral sites by Fe3 + . Hyperfine fields of 505 and 477 kOe in pure CoFe2O4 have been found for China magnets octahedral and tetrahedral sites respectively at liquid nitrogen temperature. The hyperfine field decreases with Ag-doping which also corroborates the magnetization studies. EPR study confirms the room temperature ferromagnetic behavior for Co1 − x Ag x Fe2O4 (x = 0.2). The room temperature Mössbauer studies on x = 0.0 and 0.2 show the ferromagnetic sextets (95%) along with superparamagnetic doublet (5%). However, x = 0.6 sample shows the ferromagnetic sextets only at room temperature. Highly Ag doped samples could be useful for the fabrication of the high-density magnetic materials as well as magnetic drug delivery.http://www.chinamagnets.biz
