The longitudinal magnetic susceptibility of single crystals of the molecular magnet Mn12-acetate obeys a Curie-Weiss law, indicating a transition to a ferromagnetic phase at ∼0.9 K. With increasing magnetic field applied transverse to the easy axis, a marked change is observed in the temperature dependence of the susceptibility, and the suppression of ferromagnetism is considerably more rapid than predicted by mean-field theory for an ordered single crystal. Our results can instead be fit by a Hamiltonian for a random-field Ising ferromagnet in a transverse magnetic field, where the randomness derives from the intrinsic distribution of locally tilted magnetic easy axes known to exist in Mn12-acetate crystals, suggesting that Mn12-acetate is a realization of the random-field Ising model in which the random field may be tuned by a field applied transverse to the easy axis.
Wen, Bo; Subedi, P; Bo, Lin; Yeshurun, Y; Sarachik, M P.; Kent, A D.; Millis, A J.; Lampropoulos, Christos; and Christou, G, "Realization of Random-Field Ising Ferromagnetism in a Molecular Magnet" (2010). Chemistry Faculty Publications. 15.