Quantum-classical crossover for biaxial antiferromagnetic particles with a magnetic field along the hard axis

Abstract

Quantum-classical crossover of the escape rate is studied for biaxial antiferromagnetic particles with a magnetic field along the hard axis. The phase boundary line between first- and second-order transitions is calculated, and the phase diagrams are presented. Comparing with the results of different directed fields, the qualitative behavior of the phase diagram for the magnetic field along the hard axis is different from the case of the field along the medium axis. For the hard axis the phase boundary lines k(y) shift downwards with increasing h, but upwards for the medium axis. It is shown that the magnetic field along the hard axis favors the occurrence of the first-order transition in the range of parameters under the certain constraint condition. The results can be tested experimentally for molecular magnets Fe 8 and Fe 4.