On the first-order phase transitions in a bistable large-spin systems   (Mn12Ac and others)
  We have shown that recent report concerning the first-order phase transitions in the large-spin systems is inaccurate. A kinetic numerical method for making calculations of the transition rate in a bistable system as a function of temperature has been evolved and a new critical value of the transition field (h=0.891) has been found. A physical mechanism caused transition from quantum to classical behavior has been discussed. 
V. V. Makhro