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 due to dipolar interactions. With increasing magnetic field applied transverse to the easy axis, the transition temperature decreases considerably more rapidly than predicted by mean field theory to a T=0 quantum critical point. Our results are consistent with an effective Hamiltonian for a random-field Ising ferromagnet in a transverse field, where the randomness is induced by an external field applied to Mn12-acetate crystals that are known to have an intrinsic distribution of locally tilted magnetic easy axes.
@article{arxiv.0910.1754,
title = {Realization of random-field dipolar Ising ferromagnetism in a molecular magnet},
author = {Bo Wen and P. Subedi and Lin Bo and Y. Yeshurun and M. P. Sarachik and A. D. Kent and C. Lampropoulos and G. Christou},
journal= {arXiv preprint arXiv:0910.1754},
year = {2010}
}