The quantum mechanical tunneling of the direction of magnetization is discussed for several examples of single-molecule magnets (SMMs). SMMs are molecules that function as nanomagnets. Magnetization tunneling is described for two crystallographically different forms of [Mn12O12(O2CC6H4-p-Me)(16)(H2O)(4)].solvate. The two Mn-12 complexes are isomers, differing both in the positioning of the H2O and carboxylate ligands and also in the orientations of the Jahn-Teller elongation at the Mn-III ions. The magnetization vs magnetic field hysteresis loops are quite different for the two isomeric Mn-12 complexes. Frequency-dependent ac magnetic susceptibility and dc magnetization decay data are presented to characterize the magnetization relaxation rate vs temperature responses of two mixed-valence Mn-4 complexes. In both cases the Arrhenius plot of the logarithm of the magnetization relaxation rate vs the inverse absolute temperature shows a temperature-dependent region as well as a temperature-independent region. (C) 2002 American Institute of Physics.
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