Magnetic properties of nanostructured ferrimagnetic zincferrite

Abstract

Nanostructured ZnFe2O4 ferrites with different grain sizeswere prepared by high energy ball milling for various milling times. Both theaverage grain size and the root mean square strain were estimated from thex-ray diffraction line broadening. The lattice parameter initially decreasesslightly with milling and it increases with further milling. The magnetizationis found to increase as the grain size decreases and its large value isattributed to the cation inversion associated with grain size reduction. The57Fe Mössbauer spectra were recorded at 300 K and 77 K for thesamples with grain sizes of 22 and 11 nm. There is no evidence for thepresence of the Fe2+ charge state. At 77 K the Mössbauer spectraconsist of a magnetically ordered component along with a doublet due to thesuperparamagnetic behaviour of small crystalline grains with thesuperparamagnetic component decreasing with grain size reduction. At 4.2 K thesample with 11 nm grain size displays a magnetically blocked state as revealedby the Mössbauer spectrum. The Mössbauer spectrum of this sample recordedat 10 K in an external magnetic field of 6 T applied parallel to the directionof gamma rays clearly shows ferrimagnetic ordering of the sample. Also, thesample exhibits spin canting with a large canting angle, maybe due to aspin-glass-like surface layer or grain boundary anisotropies in the material.