Investigation of superparamagnetism in pure and chromium substituted cobalt nanoferrite

•Particle size of CoFe2O4 and CoCr0.9Fe1.1O4 is 6.5 nm and 10.7 nm respectively.•At 5 K and 25 K the materials were ferromagnetic in nature with high coercivity.•Materials show superparamagnetic behavior above room temperature.•Blocking temperature is at around 355 K where coercivity and remanence are zero.•Materials are suitable for hyperthermia cancer therapy.

Nanostructured magnetic materials with the chemical composition CoFe2O4 and CoCr0.9Fe1.1O4 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 (Tb) 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. CoCr0.9Fe1.1O4 nanoferrites with observed low coercivity of 338 Oe make them desirable in high frequency transformers due to their very soft magnetic behavior.