QUANTUM-CLASSICAL PHASE TRANSITION OF THE ESCAPE RATE OF TWO-SUBLATTICE ANTIFERROMAGNETIC LARGE SPINS

The Hamiltonian of a two-sublattice antiferromagnetic spins, with single (hard-axis) and double ion anisotropies described by is investigated using the method of effective potential. The problem is mapped to a single particle quantum-mechanical Hamiltonian in terms of the relative coordinate and reduced mass. We study the quantum-classical phase transition of the escape rate of this model. We show that the first-order phase transition for this model sets in at the critical value Jc = (Kc+Jz, c)/2 while for the anisotropic Heisenberg coupling we obtain Jc = (2Kc-Jz, c)/3. The phase diagrams of the transition are also studied.