Quantum spin dynamics in mesoscopic magnets

Molecular magnets present a new class of systems that can exhibit macroscopic quantum coherence. We show that magnetic fields can induce controllable tunnel barriers for the Neel vector in antiferromagnets such as the ferric wheel. The tunneling dynamics manifests itself in e.g. NMR resonances, the static magnetization or the specific heat. Numerical simulations confirm and complement the analytical results based on an extended non-linear sigma model. (C) 1997 Elsevier Science B.V. All rights reserved.