Macroscopic quantum tunneling of ferromagnetic domain walls

Quantum tunnelling of domain walls out of an impurity potential in a mesoscopic ferromagnetic sample is investigated. Using improved expressions for the domain-wall mass and for the pinning potential, we find that the crossover temperature between thermal activation and quantum tunnelling is of a different functional form than found previously. In materials such as Ni or yttrium iron garnet, the crossover temperatures are around 5 mK. We also find that the WKB exponent is typically two orders of magnitude larger than current estimates. The sources for these discrepancies are discussed, and precise estimates for the transition from three-dimensional-to-one-dimensional magnetic behavior of a wire are given. The crossover temperatures from thermal-to-quantum transitions and tunnelling rates are calculated for various materials and sample sizes.