Site preference of Fe in nanoparticles of ZnFe2O4

Nanoparticles of ZnFe2O4, prepared by both high-energy ball milling and sol-gel methods, have been investigated by X-ray diffraction and Mossbauer spectroscopy. These results are compared with those for the bulk material. Mossbauer measurements which cover the temperature range 4.2 K to room temperature were acquired in zero field and an applied magnetic field of 5 T. The results show that the Neel temperature T-N of bulk ZnFe2O4 is about 9 K, whereas for the nanoparticle it is much higher; furthermore the transition temperature for particles of the same size depends on the preparation technique. The likely origin for this increase of TN, in the nanoparticles, namely the redistribution of Fe and Zn cations on the A and B sites, is proposed and discussed. (C) 2003 Elsevier B.V. All rights reserved.