Andrew Boothroyd

Abstract:

Neutron spectroscopy has been used to study the crystal field excitation spectra in high quality samples of RBa(2)Cu(4)O(8) high temperature superconductors, with R = Dy, Ho and Er. The samples were prepared under high oxygen pressure. Analysis of the spectra included treatment of the spin-orbit and Coulomb interactions, sad yielded crystal field parameters which showed a high degree of consistency from one rare earth to another.

Abstract:

We have studied the temperature dependence of crystal field (CF) excitation linewidths of lanthanide ions (Er and Ho) in YBa(2)Cu(3)0(7) by neutron scattering. The Ho data reveal an anomaly in the CF damping around T-c with no evidence of a coherence peak below T-c. We have applied the theory of Becker, Fulde and Keller to derive the reduced s-f coupling constants from the CF linewidth data for the ions Er, Ho and Tm.

Abstract:

We have studied the magnetic ordering of the Cu and Pr ions in PrBa2Cu3O6+x by neutron diffraction on single crystals with different oxygen contents. Two types of Cu ordering were observed, qualitatively similar to the anti-ferromagnetic phases reported in some studies of YBa2Cu3O6+x. A third magnetic structure was observed below 15K, which we believe corresponds to the magnetic ordering of the Pr sub-lattice.