Investigation of the Brownian relaxation and hydrodynamic radius in magnetic nanoparticles

Magnetic resonance is used to estimate the Brownian relaxation time and hydrodynamic radius of MnFe2O4 ferrite nanoparticles in suspension in a magnetic fluid. By measuring the resonance linewidth broadening as a function of the particle-particle distance and as a function of the temperature, relaxation time and hydrodynamic radius respectively of the order of 4.8 mu s and 11.7 nm were estimated. The relaxation time falls within the expected range and the hydrodynamic radius is found to be 2.2 times the mean value of the particle radius (5.4 nm), in excellent agreement with the literature. (C) 1997 Elsevier Science Ltd.