Magnetic excitations of a Heisenberg spin glass : evidence for a gap in high magnetic fields C. Marcenat, A. Benoit, A. Briggs, C. Arzoumanian, A.M. De Goer et F. Holtzberg J. Physique Lett., 46 12 (1985) 569-574 DOI: 10.1051/jphyslet:019850046012056900