Dissipation by nuclear spins in macroscopic magnetization tunneling

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Abstract
Magnetic systems are currently considered attractive candidates in which to look for quantum phenomena such as the tunneling of the total magnetization of a small (∼100 Å diameter) particle out of a metastable easy direction or between degenerate easy directions. The effect of nuclear spins as a dissipative environment for such a particle is considered and shown to be significant. Two dimensionless parameters characterize the dissipation: a coupling strength varying as the number of nuclear spins, and the ratio of the nuclear and electronic Larmor frequencies.