Crossover between first- and second-order transitions of a spin tunneling in a magnetic field

Based on the spin-coherent state path integral, we have considered the quasiclassical escape rate transition for the nano-spin system. Expanding the period of the classical motion in the imaginary time around the top of the potential barrier, we have presented the boundary between the first- and the second-order transition, and the corresponding crossover temperature for the uniaxial and the biaxial spin system. (C) 2000 Elsevier Science B.V. All rights reserved.