1. W. Marshall and S.W. Lovesey “Theory of Thermal Neutron Scattering”, Clarendon, Oxford (1971), p. 176.
2. G. Dolling, in “Lattice Dynamics and Intermolecular Forces”, Academic Press, New York (1975).
3. H.A. Mook and D. Tocchetti, Phys. Rev. Lett. 43: 2029 (1979).
4. J.F. Cooke and H.L. Davis, in “Magnetism and Magnetic Materials - 1972”, C.D. Graham, Jr., and J.J. Rhyne, eds., AIP, Conference Proceedings No. 10, American Institute of Physics, New York, (1972) p. 1218.
5. Y. Ishikawa, G. Shirane and J.A. Tarvin, Phys. Rev. B16: 4956 (1977).