Andrew Boothroyd

Abstract:

Neutron spectroscopic measurements of the magnetic excitations in PrO2 reveal (1) sharp peaks characteristic of transitions between levels of the 4f(1) configuration of Pr4+ split by the cubic crystal field, and (2) broad bands of scattering centered near 30 and 160 meV. We present a simple model based on a vibronic Hamiltonian that accounts for these contrasting features of the data. The analysis shows that 90%+/-10% of the Pr ions have a localized 4f(1) configuration and provides strong evidence for a dynamic Jahn-Teller effect in the gamma(8) electronic ground state.

Abstract:

I give a short review of neutron and X-ray scattering experiments undertaken to study the magnetic properties of non-superconducting PrBa2Cu3O6+x. The measurements have confirmed the magnetic ordering of the Pr sublattice at temperatures below T-Pr approximate to 20 K, and have revealed an incommensurate magnetic structure with a long period (similar to 600 Angstrom) involving both the Pr and Cu spins. The Cu spins in this Pr ordered phase are found to be non-collinear. Taken as a whole, the results provide strong evidence for a substantial magnetic coupling of the pseudodipolar type between the Pr and Cu ions. The effect of this coupling is also evident in the spectrum of low energy magnetic excitations determined by neutron inelastic scattering. (C) 2000 Elsevier Science S.A. All rights reserved.