Andrew Boothroyd

Abstract:

We report on the extension of resonant magnetic diffraction into the soft X-ray region (500-1500eV). We conducted soft X-ray diffraction from a bulk single crystal of La2-2xSr1+2xMn2O7 using an in-vacuum diffractometer. We demonstrate that the resonant enhancement diffraction of the (001) magnetic peak at the manganese L-III and L-II absorption edges is extremely large. Measurements taken on samples with different strontium dopings demonstrate that the shape of the energy resonance is also dependent on the sample stoichiometry. We have applied this technique to the study of other materials such as UAs1-xSex where incommensurate magnetic diffraction has been observed at the uranium N-IV and N-V edges. (C) 2003 Elsevier B.V. All rights reserved.

Abstract:

We report measurements of the phonon dispersion relations in nonsuperconducting, oxygen-deficient PrBa2Cu3O 6+x (x ≈ 0.2) by inelastic neutron scattering. The data are compared with a model of the lattice dynamics based on a common interatomic potential. Good agreement is achieved for all but two phonon branches, which are significantly softer than predicted. These modes are found to arise predominantly from motion of the oxygen ions in the CuO2 planes. Analogous modes in YBa2Cu3O6 are well described by the common interatomic potential model.

Abstract:

We report magnetization and neutron scattering measurements of the half-doped compound La1.5Sr0.5CoO4, which exhibits a checkerboard pattern of charge ordering below not, vert, similar800 K. In the antiferromagnetically-ordered phase below not, vert, similar40 K the spins are found to be canted in the ab plane. The spin excitation spectrum includes spin-wave excitations with a maximum energy of 16 meV, and diffuse magnetic modes at energies around 30 meV.