Relaxation and Landau-Zener experiments down to 100 mK in ferritin

Temperature-independent magnetic viscosity in ferritin has been observed from $\ensuremath{\sim}2 \mathrm{K}$ 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 $\ensuremath{\alpha}=dH/dt$ ranging from ${10}^{\ensuremath{-}5}$ to ${10}^{\ensuremath{-}3} \mathrm{T}/\mathrm{s}$ and at different temperatures from 150 mK up to the blocking temperature. We propose a $T\mathrm{ln}(\ensuremath{\Delta}{H}_{\mathrm{eff}}/{\ensuremath{\tau}}_{0}\ensuremath{\alpha})$ scaling law for the Landau-Zener probability in a system distributed in volumes, where $\ensuremath{\Delta}{H}_{\mathrm{eff}}$ is the effective width of the zero-field resonance.