Book Description

(Uncorrected OCR) Abstract of thesis entitled MACROSCOPIC QUANTUM PHENOMENON IN MOLECULAR MAGNETS submitted by Hu Jianming for the Degree of Master of Philosophy at The University of Hong Kong in July 2003 Richard Feynman said that physical laws do not imply any limitation on our ability to construct and assemble objects at the atomic scale. Since compact and well-constructed materials can make functional devices smaller and more effective, considerable efforts have been made to synthesize better materials. Single molecular magnets(SMMs), in which molecular clusters are usually fixed in the crystal and have well isolated structures, become excellent candidates in building such kind of materials. Typically, molecular magnets have large uniaxial magnetic anisotropy which form energy barriers and force the spin of the molecules be either up or down. In the absence of the external magnetic field, the energy of states with spin up and spin down degenerates. Such degeneracy is removed under the influence of the external magnetic field. For several specific external magnetic fields, energy splitting can be found around the resonant points. The energy splitting between the states may induce quantum tunnelling which produces a sudden change in the magnetization of the samples. Thanks to the highy-sensitive techniques, such as micro-SQUID and HF-EPR etc., energy splitting can be determined quantitatively in experiments with extremely high precision. In present thesis, several experimental techniques are introduced briefly, and then a specific discussion on the three SMMs and the dimer of SMMs. The importance of the second and the forth order terms on inducing the energy splitting is identified by our numerical calculations. In addition, comparison between the theoretical and numerical periods of the quantum phase interference on several SMMs is performed. The newly synthesized dimer of SMMs does provide us a good chance to discuss the interaction between the molecular cluster.