Effect of size and synthesis route on the magnetic properties of chemically prepared nanosize ZnFe2O4

Magnetization of the ZnFe2O4 sample of average size 4nm measured with SQUID in the temperature range 5-300K shows anomalous behaviour in field cooled (FC) and zero-field-cooled (ZFC) conditions. The FC and ZFC curves measured in 50Oe field cross each other a little before the peaks. No such anomaly is observed with samples of 6nm particle size made with the same procedure. The characteristics of the FC and ZFC curves are very different in ZnFe2O4 samples of the same size (6nm) made via two different chemical routes. The genesis of these differences are suggested to be in cationic configuration and spin disorder. Fe-extended X-ray absorption fine structure (EXAFS) studies show that there is around 80% inversion in case of zinc ferrite (ZnFe2O4) with the particle size 4nm, whereas ZnFe2O4 of size 6nm shows 40% inversion. The samples with an average particle size of 7nm and more show negligible inversion. Theoretical simulations suggest that the electrostatic energy of the system plays a crucial role in deciding the cationic configuration of spinel ferrites.