ESCAPE RATE TRANSITIONS IN THE Fe8 MOLECULAR MAGNET WITH FOURTH-ORDER TRANSVERSE ANISOTROPY.

We study escape rate transitions in the Fe8 molecular magnet with fourth-order transverse anisotropy in the presence of an external field perpendicular to the easy axis. Direct numerical diagonalization has been employed to investigate the transition type and the transition temperature T0. We find that the first-order transition as well as the second-order transition can exist when the field is applied along the hard axis, while only the second-order transition appears for the field along the medium axis. It is also observed that the transition temperature is increased due to fourth-order transverse anisotropy. [ABSTRACT FROM AUTHOR]