High speed coherent switching below the Stoner-Wohlfarth limit

Measurements of the switching characteristics of high coercivity magnetic tapes for field pulse widths /spl ges/0.6 ns have been reported previously. In an effort to develop a simple theoretical framework in which to develop a simple magnetization dynamics, the well established Gilbert form of the Landau-Lifshitz equation, applied to a uniaxial, single domain particle with uniform magnetization was chosen. The results which were obtained using straightforward numerical methods show that when the damping constant /spl alpha/<1, coherent switching will sometimes occur well below the Stoner-Wohlfarth threshold. The amount of deviation which is significant over a wide range of experimentally observable parameters increases as /spl alpha/ and the pulse rise time decrease. The deviation is due to the nonequilibrium condition which arises for small values of /spl alpha/ pulse rise time. The final position is always the expected Stoner-Wohlfarth equilibrium position.<
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