Quasi-elastic neutron scattering on

Magnetodynamics of ferrofluid γ-$\rm Fe_2O_3$ nanoparticles is studied by Quasi-Elastic Neutron Scattering between 10 K and 250 K in the frequency range 1010–$\rm 10^{12}\; Hz$. 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