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- Title
Instanton Paths for the Problem of Coherent Quantum Tunneling in Small Ferromagnetic Particles.
- Authors
Ivanov, B. A.; Kulagin, N. E.
- Abstract
It is shown that the problem of instantons in ferromagnetic materials in a large-spin model is reduced to an exactly integrable dynamical system with a finite number of variables. For a rather wide class of models, there exists a continuum of instanton paths that form a one-parameter family of paths with essentially different shapes but with the same value of the Euclidean action. On the basis of the formalism developed, exact instanton solutions are constructed that describe macroscopic quantum tunneling for a small ferromagnetic particle with uniaxial or biaxial quadratic anisotropy in the presence of a magnetic field applied perpendicularly to the easy axis. These solutions are valid for any relations between the anisotropy parameters and for any magnitude of the magnetic field and its direction in the base plane. Based on the solutions obtained, the principles of macroscopic quantum tunneling in high-spin-molecule-type magnetic particles are described. Tunneling regimes of two types are obtained: (1) regimes that are characterized by destructive interference of instanton trajectories and oscillatory dependence of the transition probability on the magnitude of the magnetic field and (2) regimes in which all instantons have the same purely real value of the Euclidean action and there is no destructive interference. © 2004 MAIK “Nauka/Interperiodica”.
- Subjects
FERROMAGNETIC materials; MAGNETIC materials; FERROMAGNETISM; MAGNETISM; MAGNETICS
- Publication
Journal of Experimental & Theoretical Physics, 2004, Vol 99, Issue 6, p1291
- ISSN
1063-7761
- Publication type
Article
- DOI
10.1134/1.1854816