Investigating the Langevin behaviour of Faraday rotation in soft ferrimagnetic CoFe2O4 nanoparticles dispersed in PVA-water medium

Abstract

Soft ferrimagnetic (FM) cobalt ferrite, CoFe2O4 (CoF) nanoparticles (NP) were synthesized using chemical co-precipitation technique. The constraint related to forming stable dispersion of the synthesized NP was successfully overcome by using an efficient dispersing medium namely, a 2 Wt% Polyvinyl Alcohol (PVA) - water solution, the PVA molecules of which played an important role in offering excellent stability by preventing the agglomeration of the NP considerably. Magneto-optic Faraday Rotation (MOFR) studies performed on the prepared stable dispersions at 532 nm laser wavelength for applied magnetic fields upto 2400 Oe indicated a Langevin behaviour consistent with the chain/cluster formation in them. The studies were carried out at two different concentrations, where the saturated value of MOFR, Bs , was higher for the more concentrated sample, while the saturation magnetic field, HS , followed the reverse trend. It was interesting to see that HS , was as large as 1800 Oe for the concentrated sample, and still higher for the less concentrated one, which may be due to an obstruction effect due to PVA molecules, which delay the formation and saturation of NP chains. The MOFR studies in soft FM NP dispersions open up an interesting domain, both for fundamental understanding of physical phenomena as well as for applications.