1. Excitations in Magnetic Systems with a Singlet Ground State
2. Birgeneau, R.J., In: Magnetism and Magnetic Materials 1972 (Edited by C. D. Graham, Jr. and J. J. Rhyne), AIP Conference Proceedings, to be published.
3. The bulk properties of such a Hamiltonian and its application to interpret the excitation spectrum of d.h.c.p. Pr have been studied and submitted for publication elsewhere.