NEW DOUBLE MAGNON MODES IN PLANAR ANTIFERROMAGNETIC CHAINS IN A FIELD J. P. Boucher, M. Remoissenet, R. Pynn and L. P. Regnault J. Phys. Colloques, 49 C8 (1988) C8-1381-C8-1382 DOI: 10.1051/jphyscol:19888633