EFFECT OF MAGNETIC-ORDERING ON THE LOW-ENERGY EXCITATIONS OF R2BANIO5(R = HO, ER) STUDIED BY NEUTRON AND OPTIC SPECTROSCOPIES

The crystal field (CF) levels of the ground state multiplets of Ho and Er in R2BaNiO5 have been studied combining inelastic neutron scatteri ng and photoluminescence experiments at temperatures above and below t he 1D to 3D magnetic transitions (at 53 and 32 K, respectively) at whi ch the Ni and R sublattices order antiferromagneticaly. In Ho compound 3D magnetic peaks have been detected well above T-N. Energy shift and splitting of several Kramers doublets is observed in Er compound belo w the magnetic transition due to the local magnetic field at Er sites. No dispersion is detected for the CF transitions. The evolution with temperature of the energy and width of the inelastic and elastic peaks is investigated. The lowest R3+ crystal field levels have been obtain ed in Ho compound at 0, 1.3, 2.7, 11.6 and 18.1 meV and in Er compound at 0, 4.9, 8.2, 10.4 and 16.6 meV above T-N. (C) 1998 Elsevier Scienc e B.V. All rights reserved.