INTERACTION OF A SPIN WITH THE EXTERNAL WORLD AT LOW TEMPERATURE
The fundamental aspects of coherence, incoherence, and relaxation, which characterize the interaction of a molecular spin with the external world, are worked out. The effects determined by the presence of magnetic nuclei are discussed by introducing the hyperfine interaction. The experimental evidence of hyperfine interactions on the quantum dynamics of the magnetization is reported for Fe8 crystals in natural abundance of magnetic isotopes, and in 57Fe and 2H enriched samples, respectively. The hole digging procedure used in the experiments is discussed, as well as the mechanism of relaxation induced by hyperfine interactions. The relaxation associated with dipolar interactions between molecular spins is considered, and the square root time dependence of the relaxation is worked out. Experimental evidence is reported, and other theoretical approaches, including the Caldeira Leggett theory, are presented.
Keywords: coherence, magnetic relaxation, hyperfine interactions, magnetic nuclei, isotope effect, square root relaxation, Caldeira Leggett theory
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