Magnetic properties of nanostructured ferrimagnetic zinc ferrite

Nanostructured ZnFe2O4 ferrites with different grain sizes were prepared by high energy ball milling for various milling times. Both the average grain size and the root mean square strain were estimated from the x-ray diffrac tion line broadening. The lattice parameter initially decreases slightly wi th milling and it increases with further milling. The magnetization is foun d to increase as the grain size decreases and its large value is attributed to the cation inversion associated with grain size reduction. The Fe-57 Mo ssbauer spectra were recorded at 300 K and 77 K for the samples with grain sizes of 22 and 11 nm. There is no evidence for the presence of the Fe2+ ch arge state. At 77 K the Mossbauer spectra consist of a magnetically ordered component along with a doublet due to the superparamagnetic behaviour of s mall crystalline grains with the superparamagnetic component decreasing wit h grain size reduction. At 4.2 K the sample with 11 nm grain size displays a magnetically blocked state as revealed by the Mossbauer spectrum. The Mos sbauer spectrum of this sample recorded at 10 K in an external magnetic fie ld of 6 T applied parallel to the direction of gamma rays clearly shows fer rimagnetic ordering of the sample. Also, the sample exhibits spin canting w ith a large canting angle, maybe due to a spin-glass-like surface layer or grain boundary anisotropies in the material.