QUANTUM TUNNELING OF MAGNETIZATION IN SINGLE-DOMAIN COFE2O4 PARTICLES

We systematically investigated the macroscopic quantum tunneling (MQT) phenomena of magnetization in CoFe2O4 particles with a diameter rangi ng from 30 to 92 Angstrom in zero external magnetic field to remove th e substantial influence of energy dissipation. For all of our samples, we observed the MQT phenomena in zero external magnetic field, in spi te of the anticipation that a large magnetic field H comparable with t he coercive force H-c would be necessary to lower the energy barrier s o as to observe appreciable quantum tunneling of magnetization. The an alysis shows that the crossover temperature T from the thermal to the quantum regime increases with decreasing anistropy field H-A. This re lation between T and H-A is inconsistent with the theoretical predict ion.