Quantum-classical crossover of the escape rate for ferric wheels with excess spin

Quantum-classical crossover of the escape rate is studied for ferric wheels with excess spin, in which one of the Fe (III) ions has been replaced by a dopant ion. Using nonlinear perturbation method, the formula of the phase boundary line between first- and second-order transitions is derived. In the high field regime for Néel vector tunneling scenario, with the characteristic parameters of the ferric wheels Fe10, Cs:Fe8, Li:Fe6, and Na:Fe6, it is shown that quantum-classical crossover of the escape rate for ferric wheels with excess spin is the second-order transition.