Coherent Magnetic Moment Reversal in Small Particles With Nuclear Spins

Abstract

A discrete WKB method is developed for calculating tunnel splittings in spin problems. The method is then applied to the issue of how nuclear spins affect the macroscopic quantum coherence of the total magnetic moment in small magnetic particles. The results are compared with numerical work, and with previous instanton based analytic approaches.

Application of the discrete Wentzel–Kramers–Brillouin method to spin tunneling

“…Our answers for ∆ 0 agree completely with those of Enz and Schilling [7], or Belinicher, Providencia, and Providencia [13], and we believe they are obtained with much less effort. While the discrete WKB method does not have the nice geometrical structure of the spin-coherent-state path integral approach, it provides compensation in that it yields wavefunctions in the course of the calculation, which may be of further use; for evaluating matrix elements of perturbations, for example [20,21]. Other problems commonly solved by the continuous WKB method, such as escape from a metastable well, are also amenable to the method, but we do not discuss these here.…”