TEMPERATURE-DEPENDENCE OF MACROSCOPIC QUANTUM TUNNELING IN ANTIFERROMAGNETIC PARTICLES

By explicit calculation of quantum tunneling at the level of excited s tates in a model of an antiferromagnetic particle, it is demonstrated that the transition through the potential barrier may be subdivided in to three distinct regions: the ground state tunneling region, the ther mally assisted tunneling region and the thermal activation region. The numerical result that the tunneling rate is independent of temperatur e in the first region agrees with the experimental observation reporte d by Tejada and Zhang [J. Phys. Condens. Matt. 6 (1994) 263]. (C) 1998 Elsevier Science B.V.