QUANTUM TUNNELING OF MAGNETIZATION IN MESOSCOPIC SYSTEMS

Mesoscopic systems provide a unique opportunity for the study of the p henomenon of quantum tunneling of magnetization (QTM). This phenomenon is a macroscopic quantum tunneling effect in which the magnetization vector undergoes quantum underbarrier transitions which manifest thems elves as temperature independent magnetic relaxation. The study of thi s relaxation at very low temperatures affords the opportunity to study the phenomenon experimentally. Low temperature relaxation will be dis cussed in a variety of mesoscopic systems. Data will be presented for logarithmic and exponential relaxation to demonstrate the occurrence o f QTM. At high temperatures the relaxation shows the temperature depen dence. Below a certain temperature, called the crossover temperature, T-c, the relaxation becomes independent of temperature. These data agr ee qualitatively with the recent theoretical work on QTM. We will conc lude the paper with the recent work on polynuclear high spin molecules where we have observed thermally assisted resonant tunneling processe s between degenerate spin levels of opposite orientation. (C) 1997 Act a Metallurgica Inc.