INVESTIGATION OF THE BROWNIAN RELAXATION AND HYDRODYNAMIC RADIUS IN MAGNETIC NANOPARTICLES

Magnetic resonance is used to estimate the Brownian relaxation time an d hydrodynamic radius of MnFe2O4 ferrite nanoparticles in suspension i n 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 t o be 2.2 times the mean value of the particle radius (5.4 nm), in exce llent agreement with the literature. (C) 1997 Elsevier Science Ltd.