Dynamical Spin Hamiltonian and the Anisotropy of Spin-Lattice Relaxation for the Kramers Doublets. I. General Considerations

Abstract

The limitations of a previous treatment of the dynamical spin Hamiltonian in relation to Kramer's doublets have been pointed out. It is shown that the momentum operators in addition to the symmetry coordinates must be included in the dynamical spin Hamiltonian for such systems. The most important effect of this inclusion is the appearance of the Zeeman-field-independent Van Vleck two-phonon terms which account for most of the spin-lattice relaxation in such systems at high temperature. The anisotropy of the spin-lattice relaxation expected from such a term for crystals of various symmetries has been derived from straightforward symmetry considerations.