Investigation of superparamagnetism in pure and chromium substituted cobalt nanoferrite

Nanostructured magnetic materials with the chemical composition CoFe2O4 and CoCr0.9Fe11O4 were synthesized through Citrate-gel chemical synthesis with a crystallite size of 6.5 nm and 10.7 nm respectively. Structural characterization of the samples was performed by X-ray diffraction analysis and magnetic properties were studied using Vibrating Sample Magnetometer (VSM). Magnetization measurements as a function of applied magnetic field +/- 10 T at various temperatures 5 K, 25 K, 310 K and 355 K were carried out. Field cooled (FC) and Zero field cooled (ZFC) magnetization measurements under a magnetic field of 100 Oe for temperature ranging from 5-400 K were studied. The blocking temperature (T-b) for both the ferrites was observed to be around 355 K. Below blocking temperature they showed ferromagnetic behavior and above which they are superparamagnetic in nature that favors their application in the biomedical field. The substitution of paramagnetic Cr3+ ions for magnetic Fe3+ ion in cobalt ferrite has resulted in a decrease in magnetization and the coercivity of the samples. CoCr0.9Fe11O4 nanoferrites with observed low coercivity of 338 Oe make them desirable in high frequency transformers due to their very soft magnetic behavior. (C) 2016 Elsevier B.V. All rights reserved.