Se p 20 01 Relaxation and Landau - Zener experiments down to 100 mK in Ferritin

Temperature-independent magnetic viscosity in ferritin has been observed from ∼ 2 K down to 100 mK, proving that quantum tunneling plays the main role in these particles at low temperature. Magnetic relaxation has also been studied using the Landau-Zener method making the system crossing zero resonant field at different rates, α = dH/dt, ranging from 10 −5 to 10 −3 T/s, and at different temperatures, from 150 mK up to the blocking temperature. We propose a new T ln(∆H ef f /τ 0 α) scaling law for the Landau-Zener probability in a system distributed in volumes, where ∆H ef f is the effective width of the zero field resonance.