Study of Different Ferrofluid Systems by Electron Paramagnetic Resonance Technique: A Review

Abstract

Magnetic fluids have been receiving considerable importance due to their wide range of technological applications in the domain of nano - structured material. In such fluids magnetic particles are randomly dispersed in carrier fluid and resembles like a paramagnetic gas. In this paper we reviewed our earlier EPR work on different ferrot1uid systems viz. ionic ferrofluid, ferrofluid - conducting polymer composite, magnetite particles dispersed in PVA polymer

matrix composite films. Single domain Fe₃O₄magnetic particles of size 10 to 100 Ǻ are dispersed in carrier fluid like water, diester, paraffin and other liquid hydrocarbons and are similar to colloidal state. In these ferrofluids, EPR spectra showed a single, isotropic broad line spectra at all temperatures. At low temperatures, line width of the signal increases with the decrease in g-value. This may be due to the increase in viscosity of the carrier fluid at low

temperatures which locks the spin direction and rotation of magnetic particles and hinders their bulk rotation. In ionic ferrofluid, due to freezing of water with local expansion leads to the randomization of spins and formation of new spin glass or cluster glass states. In all these EPR recorded spectra at different low temperatures, we have not obtained signal pertaining to superparamagnetic state. The reason for this may be non - availability of magnetic

particles smaller than critical size and their desired concentration. In conducting polymer - ferrofluid composite, EPR signal was much broader than pure ferrot1uid which was attributed to the decrease in dipole - dipole interaction due to the bonding of magnetic particles with polymer chains and increase in distance between them. While magnetite particles dispersed in PVA polymer matrix thin films, were grown in the absence and presence of magnetic field. In these composites also a broad line EPR signal was obtained for both types. The change in line width and intensity confirms the orientation of magnetic domains in film network.