Tb spin correlations in Pb 2 Sr 2 Tb 0.5 Ca 0.5 Cu 3 O 8

Abstract
High-resolution neutron spectroscopy and neutron diffraction results on the magnetic properties of Tb in the high-Tc superconductor Pb2Sr2Tb0.5Ca0.5Cu3O8 are presented. The lowest-lying crystalline-electric-field transition, expected at 7 μeV, is not observed, indicating that the system can still be described in the mean-field approximation at 20 K, well above TN (4 K). The inelastic neutron spectra can be decomposed into an elastic and a quasi-elastic part, indicating that a single Lorentzian does not describe well the magnetic-response function and/or that Tb 2D short-range correlations persist up to temperatures above 100 K.