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

Magnetization of the ZnFe₂O₄ sample of average size 4 nm measured with SQUID in the temperature range 5–300 K shows anomalous behaviour in field cooled (FC) and zero-field-cooled (ZFC) conditions. The FC and ZFC curves measured in 50 Oe field cross each other a little before the peaks. No such anomaly is observed with samples of 6 nm 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 (6 nm) 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 4 nm, whereas ZnFe₂O₄ of size 6 nm shows 40% inversion. The samples with an average particle size of 7 nm 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.