The dynamical properties of the magnetic moment of non-interacting cobalt nanoparticles dispersed in a polymer were investigated by ac-susceptibility (10 Hz < f < 104 Hz). We thus estimated the relaxation time of the magnetisation (τ) associated to the superparamagnetic properties of the particles, τ was found to follow the general Néel-Brown relaxation dynamics, with a pre-exponential relaxation time τ0 of 4(±2)·10-12 s for temperatures between 10 and 20 K. By combining the experimental results from ferromagnetic resonance, ac-susceptibility, and magnetisation, measurements giving the microscopic and macroscopic parameters, we demonstrate for the first time that the Coffey theoretical expressions were able to predict both τ and τ0 values. Finally, the thermal dependence of τ0 is discussed.
ASJC Scopus subject areas
- Physics and Astronomy(all)