SPIN DYNAMICS OF ER-3+ IN ERBA2CU3O7-DELTA

Neutron scattering techniques are used to study the magnetic excitatio ns of the Er ions in superconducting ErBa2Cu3O7, a system where the Er ions order antiferromagnetically at T-N = 0.62 K and the sublattice m agnetization obeys the relation for a 2D S = 1/2 Ising model. Our data , which were taken on a cold neutron triple axis spectrometer using a horizontally focusing analyzer, reveal that there is a large gap of ab out 0.20 meV in the excitation spectrum, about four times the thermal energy kT(N), as expected for an Ising system. However, we also observ e dispersion of the spin waves in the a-b plane. These excitations are found to renormalize with temperature and only diffuse paramagnetic s cattering is observed well above the ordering temperature. (C) 1997 Am erican Institute of Physics.