Experimental observation of quantum coherence in molecular magnetic clusters with half-integer spin

From field-dependent specific heat studies we conclude that magnetic relaxa tion becomes temperature independent for two Mn, compounds, below some temp erature T-Q. At low temperatures, the specific heal gives evidence for the presence of a tunnel splitting Delta (t) of the ground state S-z = +/- 9/2 for both compounds. The predicted quenching of Delta (t) for clusters with half-integer spin apparently does not occur, probably due to the joint acti on of dipolar and hyperfine fields, in combination with the applied perpend icular field of sufficient strength. (C) 2001 Elsevier Science Ltd. All rig hts reserved.