Nanocrystallite size effect on σs and Hc in nanoparticle assemblies

This article presents how Ni0.35Zn0.65Fe2O4 mixed ferrite nanocrystallites are obtained at low temperatures (500 deg. C) by a new chemical method of synthesis, as well as the effect of the nanocrystallites' size on the magnetic properties. We have shown by means of X-ray diffraction that the resulting ferrite is made up of nanocrystallites and the average size of these nanocrystallites - calculated with the Scherer formula - depends on the annealing temperature. When the temperature is modified from 500 deg. C to 900 deg. C, the nanocrystallites' average diameter ranges from 20.3 to 37.9 nm. The magnetic properties of the nanocrystallite assembly are discussed for values around the single-domain and the multi-domain state that results both experimentally and from theoretical calculations. The nanocrystallites are single-domain up to an average diameter of ∼29 nm, whereas above this value they have an incipient structure of Weiss domains