Europhys. Lett, 47 (2), pp. 254-259 (1999)
Nuclear-spin-driven resonant tunnelling of magnetisation in Mn12 acetate
W. Wernsdorfer 1, R. Sessoli 2 and D. Gatteschi 2
1 Laboratoire de Magnetisme Louis Néel - CNRS, BP 166, 38042 Grenoble, France
2 Dipartimento di Chimica, Università di Firenze
Via Maragliano 77, 50144 Firenze, Italy
(received 2 February 1999; accepted in final forn 19 May 1999)
PACS. 75.45+j - Macroscopic quantum phenomena in magnetic systems.
PACS. 75.50 Tt - Fine-particle systems.
PACS. 75.60 Ej - Magnetisation curves, hysteresis, Barkhausen and related effects.
Current theories still fail to give a satisfactory explanation of the observed quantum phenomena in the relaxation of the magnetisation of the molecular cluster Mn12 acetate. In the very low-temperature regime, Prokof'ev and Stamp recently proposed that slowly changing dipolar fields and rapidly fluctuating hyperfine fields play a major role in the tunnelling process. By means of a faster relaxing minor species of Mn12ac and a new experimental "hole digging'' method, we measured the intrinsic linewidth broadening due to local fluctuating fields, and found strong evidence for the influence of nuclear spins on resonance tunnelling at very low temperatures (0.04-0.3 K). At higher temperature (1.5-4 K), we observed a homogeneous linewidth broadening of the resonance transitions being in agreement with a recent calculation of Leuenberger and Loss.
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