Macroscopic quantum tunneling of the total magnetization in small ferromagnetic grains

Abstract

The tunneling of the total magnetization of a single-domain spherical (∼100-Å-diam) particle is considered for various crystal symmetries, with special attention to the dissipative effect of phonons in the grain and any embedding matrix. Such dissipation is shown to have a spectral density J(ω)∼ω3 and to be very weak. Stray fields and interparticle interactions are also considered.