Magnetocaloric effect and size-dependent study of the magnetic properties of cobalt ferrite nanoparticles prepared by solvothermal synthesis

Cobalt ferrite (CoFe2O4) nanoparticles from 2 nm to 15 nm were synthesized using a solvothermal procedure. In this nonaqueous method, acetophenone was used as solvent and the particle size was controlled by changing the reaction temperature from 120 degrees C to 180 degrees C. Nanoparticles show good crystallinity and uniformity above 140 degrees C, as determined by X-ray diffraction and transmission electron microscopy. Magnetic measurements indicate superparamagnetic behaviour. Zero-field-cooling (ZFC) dc-magnetisation experiments at 100 Oe show blocking temperatures ranging from 215 K to more than 305 K. Saturation magnetisation increases with particle size and a small decrease is observed when increasing the temperature. The magnetocaloric effect shown by these cobalt ferrite nanoparticles is reasonably high for nanomaterials. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.