PHONON DISPERSION AND TRANSVERSE MODE SOFTENING IN RbFeCl3 D. Petitgrand, B. Hennion, C. Escribe-Filippini et S. Legrand J. Phys. Colloques, 42 C6 (1981) C6-782-C6-784 DOI: 10.1051/jphyscol:19816231