Over-barrier transitions, crossover

It has been proposed that in the magnetization dynamics of singledomain particles there is a characteristic crossover temperature T below which the escape of the magnetization from the metastable states is dominated by quantum barrier transitions, rather than by thermal over barrier activation. Above T the escape rate is given by the rate of the thermal transitions, determined by the Boltzman factor, = 1/exp(—t/Z/cT), where U is the barrier separating two metastable states. In a thermally activated regime it should vanish when the temperature approaches zero. 

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