Magnetic relaxation phenomena in the erbium orthoferrite ErFeO3

We report here on low temperature magnetic relaxation in the erbium orthoferrite ErFeO 3 . The variation of magnetic viscosity, S ≡ ∂M / ∂ / ∂ ln t , with temperature shows three different regimes below 40 K. The most remarkable is that at T ≤ 3 K where S(T) remains constant suggesting the occurrence of macroscopic quantum tunneling of the magnetization.