Bifurcation of a periodic instanton and quantum-classical transition in the biaxial nano-ferromagnet with a magnetic field along hard axis

Crossover from classical to quantum regimes of the barrier transition rate in a biaxial ferromagnetic magnet with a magnetic field applied along hard anisotropy axis is investigated. We show that the type of action-temperature diagrams can he determined by counting the number of bifurcation points. The model possesses not only the known type I and Ⅱ, hut also the interesting type Ⅲ and Ⅳ of transition which do not occur in general.