Quantum exponential relaxation of antiferromagnetic domain walls in FeTbO₃ single crystal

We present the first experimental evidence of the exponential magnetic relaxation. This has been achieved in a single antiferromagnetic crystal of TbFeO₃. The existence of two relaxations regimes, thermal and quantum, is demonstrated. The low temperature escape rate can be written as Γ = ω(H)exp[ -U(H) k_BT^*(T)] with T^*(T) = T at T ≥ T_C and T^*(T) > T at T < T_C, T_C being the crossover temperature between the two regimes. From our data we have determined (with no adjustable parameters), the attempt frequency ω, the energy barrier U(H), and the WKB exponent, B. Our results are consistent with the occurrence of quantum tunneling of antiferromagnetic domain walls.