A criterion for the anisotropy barrier in single-molecule magnets

A criterion for the height of the anisotropy barrier Delta = vertical bar D vertical bar S-2 in single-molecule magnets, and therefore the blocking temperature T-B proportional to Delta, is presented. In particular, it is found that the anisotropy barrier does not increase with S as S-2 but as S-0. Consequences concerning the strategies to enhance Delta or T-B, respectively, are discussed.