Macroscopic quantum tunneling in single domain magnetic particles

Since the 1950’s there have been a number of experimental observations involving small single domain (SD) magnetic particles (≲200 Å diameter) which have been attributed to what we’d today call ‘‘macroscopic quantum tunneling’’ (MQT) of the magnetization in its switching from one easy axis direction to another. A comprehensive study of this phenomenon is not only of great interest for the sake of fundamental physics: It is of utmost practical importance in that MQT sets a limit on the lifetime of information storage on magnetic tapes and films. In this paper we present a brief summary of some of the latest results of our theoretical and experimental studies of this phenomenon.