Macroscopic quantum tunnelling in antiferromagnets

Macroscopic quantum tunnelling in a single-domain antiferromagnetic particle is considered using different models for the antiferromagnet: an effective two-spin model and an anisotropic sigma model (large-spin continuum limit of the Heisenberg Hamiltonian). For both models the probability of tunnelling at low temperatures has been calculated. The tunnelling rates obtained in these cases agree qualitatively when expressed in the terms of the corresponding quantities. The authors have also estimated the tunnelling rate for a false-vacuum decay in an antiferromagnet with a small fourth-order anisotropy.