Mn-55 NMR and relaxation studies on Mn-12-acetate

The spin-echo signals of Mn-55 in Mn-12-acetate were observed using a powde r sample in zero external field below 2.4 K in the three separate frequency ranges around 230, 280 and 370 MHz corresponding to the Mn4+ ion and to th e two inequivalent sites of Mn3+ ions, respectively. The transverse relaxat ion rate 1/T-2 exhibited a remarkable decrease over almost two orders of ma gnitude with decreasing temperature down to 1.4 K. The results were interpr eted satisfactorily by the model based on thermal fluctuations of the quant um state of the S = 10 spin of the cluster. (C) 2000 Published by Elsevier Science B.V. All rights reserved.