Macroscopic Quantum Coherence in Magnetic Molecular Clusters

The oscillation of tunnel splitting in Fe₈ molecular clusters is obtained as a function of magnetic field applied along the hard axis by means of instanton method with both semiclassical treatment and the effective potential field description of quantum spin system. The theoretical splittings of the instanton method are compared with the numerical result by diagonalization of spin Hamilton operator and experimental observations. By taking the appropriate parameters, our theory formula yields the result as the same as the experimental observation.