Spin resonance investigations on water-based magnetite ferrofluid

In this work, we have investigated a water-based ferrofluid for its magnetic properties. The nanoparticles of ferrofluid were synthesized by a chemical coprecipitation route. Magnetite nanoparticles were chemically prepared by coprecipitation of reverse micelles in the aqueous phase. A very low observed value of saturation magnetization, i.e. 1 emu/g, and the magnetic anisotropy energy constant were found in the samples. This was explained by dead layer theory and effect of double surfactant coating. Ferromagnetic resonance (FMR) measurements were performed via zero-field-cooled (ZFC) protocol. The Neel-Brown model was applied by assuming the resonance field as the applied field on the superparamagnetic system. Under these circumstances, the ratio of magnetic anisotropy energy to thermal energy was calculated and it is found that it becomes unity ~225K for the particles, which are antiparallel to the applied field.