A SIMPLE DERIVATION OF THE TUNNELING SPLITTING FOR LARGE QUANTUM SPINS

With the help of a perturbation treatment to lowest order, general exp ressions for the tunneling splitting have been derived for a quantum s pin S. This spin is assumed to have a main axial Hamiltonian (without applied longitudinal magnetic field), and to be submitted to perturbat ions with orthorhombic, tetragonal, trigonal or hexagonal symmetries, or to a transverse field. The formulas obtained are valid for general (not very small) S. They are compared with available results of the li terature. Previous observations of tunneling splittings in terbium com pounds by EPR are mentioned, with the relevant references.