Abstract
In this paper we report a comprehensive study of the low temperature magnetic relaxation of nanometer-scale antiferromagnetic horse-spleen ferritin particles. First we report on the static magnetic characterization of the sample at low and high field in the temperature interval between 4 and 300 K. Secondly, we present experimental results on the magnetic relaxation of the remanent magnetization Mr(t) associated with the uncompensated surface spins on such small particles. The magnetic viscosity S≡1/Mr[dM/d ln(t)] is proportional to temperatures above 3 K. At lower temperatures, the viscosity is independent of temperature, providing evidence to quantum tunneling of the Néel vector.