Magnetic relaxation measurements of α-Fe2O3 antiferromagnetic particles below 1 K -: art. no. 052404

In this paper we report magnetic relaxation data for anti ferromagnetic alpha-Fe2O3 particles of 5-nm mean diameter in the temperature range 0.1-25 K. The average spin value of these particles S 124 and the uniaxial anisotropy constant D similar or equal to 1.6 x 10(-2) K have been estimated from the experimental values of the blocking temperature and anisotropy field. The observed plateau in the magnetic viscosity from 3 K down to 100 mK agrees with the occurrence of spin tunneling from the ground state S-Z = S. However, the scaling M vs T In(v(0)t) is broken below 5 K, suggesting the occurrence of tunneling from excited states below this temperature.