55Mn NMR in Mn12 acetate: Hyperfine interaction and magnetic relaxation of cluster

Abstract

The 55Mn NMR in oriented powder Mn12Ac has been investigated at 1.4-2.0 K in zero field and with external fields along the c-axis. Three kinds of 55Mn NMR composed of five-fold quadrupole-split lines for I=5/2 nuclei have been interpreted to arise from Mn4+ ion, and two crystallographically-inequivalent Mn3+ ions, respectively. It is found that the isotropic hyperfine field in the Mn4+ ion with 3d3 configuration indicates a large amount of reduction (26%) as compared with the theoretical evaluation. In the analysis for the hyperfine field of Mn3+ ions with 3d4 configuration, we have taken into account of the anisotropic dipolar contribution in addition to the Fermi-contact term in order to explain two kinds of 55Mn NMR frequencies in Mn3+ ions in inequivalent sites. By using the hyperfine coupling constants of twelve manganese ions in Mn12Ac, the total hyperfine interaction of the ferrimagnetic ground state of S=10 has been determined to amount to 0.3 cm-1 in magnitude at most, the magnitude of which corresponds to the nuclear hyperfine field he(0.32 kG seen by Mn12 cluster spin. The relaxation of the cluster magnetization was investigated by observing the recovery of the 55Mn spin-echo intensity in the fields of 0.20-1.90 T along the c-axis at 2.0 K. It was found that the magnetization of the cluster exhibits the (t-recovery in the short time regime. The relaxation time decreases with increasing external field following significant dips at every 0.45 T. This is interpreted to be due to the effects of thermally-assisted quantum tunneling between the spin states at magnetic level crossings.

Text 25 pages, five figures and two tables

References in corpus (1)

• Crossover between Thermally Assisted and Pure Quantum Tunneling in Molecular Magnet Mn12-Acetate

Cited by in corpus (13)

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• Spin-Wave Description of Nuclear Spin-Lattice Relaxation in Mn_{12}O_{12} Acetate
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• Magnetic dipolar ordering and relaxation in the high-spin molecular cluster compound Mn6
• Studies of transverse and longitudinal relaxations of ${}^{55}$Mn in molecular cluster magnet Mn${}_{12}$Ac
• Semiconductive and Photoconductive Properties of the Single Molecule Magnets Mn${}_{12}$-Acetate and Fe${}_8$Br${}_8$
• Nuclear spin-lattice relaxation in ferrimagnetic clusters and chains: A contrast between zero and one dimensions
• Dynamics and thermalization of the nuclear spin bath in the single-molecule magnet Mn12-ac: test for the theory of spin tunneling
• Tunneling and inversion symmetry in single-molecule magnets: the case of the Mn12 wheel molecule
• Effect of environmental spins on Landau-Zener transitions
• Quantum Spinodal Phenomena
• Observation of zero-point quantum fluctuations of a single-molecule magnet through the relaxation of its nuclear spin bath