Macroscopic quantum tunneling and coherence of the Néel vector in small antiferromagnets

The tunneling behavior of the Néel vector out of metastable easy directions or between degener ate easy directions is studied for a small single-domain antiferromagnetic particle at low temperature. The quantum tunneling rates for these processes are evaluated for two examples of macroscopic quantum tunneling and one example of macroscopic quantum coherence. The calculations are perforrred by using the two-sublattice model and the instanton method in the spin-coherent-state path integral. Quantum interference or the spin-parity effect is also discussed for each case.