Quantum dynamics and tunneling of domain walls in ferromagnetic insulators

It is shown how large domain walls, containing ≥${10}^{10}$ spins, can behave as quantum objects at low temperatures. They move quantum diffusively, and exhibit macroscopic tunneling from defect pinning centers. The dissipation is calculated and shown to be very small; it does not involve the usual Caldeira-Leggett environmental couplings. The theory can also be used to treat smaller single-domain-wall behavior.