Proton magnetic relaxation in superparamagnetic aqueous colloids: a new tool for the investigation of ferrite crystal anisotropy

The effect of the anisotropy energy was evaluated experimentally and theoretically through the study of NMRD curves which represent the dependence of the water proton nuclear relaxation rate on the magnetic field. Evaluation of the NMRD curves of colloids made of ferrite doped with cobalt and magnetite shows that the existence of low field dispersion in the profiles indicates a low anisotropy energy. These experimental results are in agreement with the theory taking into account the Curie relaxation model and including the anisotropy energy in the Hamiltonian describing the magnetic interaction.