Magnetodynamics of ferrofluid γ-Fe₂O₃ nanoparticles is studied by Quasi-Elastic Neutron Scattering between 10 K and 250 K in the frequency range 10¹⁰–10¹² Hz. We probe independently the precession of the core magnetic moment and surface spins fluctuations observed in a dissipative regime. These fluctuations slow down at low temperature leading to a frozen disorder of the surface layer.