Electron spin resonance investigations on kerosene based magnetic fluid

A stable kerosene based ferrofluid having magnetite nanoparticles (∼10 nm) coated with oleic acid as primary was synthesized by coprecipitation route. The Rietveld refinement of XRD pattern of Fe3O4 nanoparticles was carried out using Fullprof. The Williamson-Hall method gives 10.2(3) m and 0.002(1) as average crystallite size and strain respectively. The HRTEM image shows that particles are nearly spherical in shape. The room temperature magnetic measurements shows the superparamagnetic nature of the fluid. Using modified Langevin function, the average particle size was found to be 9.8(2) nm with 0.5 as standard deviation. The low temperature ESR measurements were performed in the temperature range 4 K–300 K using zero-field cooled (ZFC) protocol. The deconvolutions of the spectra suggest coexistence of two different resonance modes; i.e., a broad resonance signal superimposed by a sharp signal. This observation is consistent for temperature range 200 K– 300 K. The behavior of resonance field, linewidth and intensity shows a characteristic spin-glass state near to 190 K.