The effect of thermal activation and quantum-mechanical tunneling on the AC-susceptibility

The ac-susceptibility χ of a ferromagnetic Ni-base alloy has been measured below 5K. The experimental data can be represented by a relation derived earlier for the unidirectional motion of 180°-domain walls. This relation is based on the assumption that the mobility of 180°-domain walls is governed by their interaction with obstacles present in the specimen. These pinning centers are overcome by combinations of thermal activation and quantum-mechanical tunneling.