X-ray and neutron scattering

Abstract:

Polarized neutron inelastic scattering has been used to measure spin excitations in ferromagnetic La0.82Sr0.18CoO3. The magnon spectrum of these spin excitations is well defined at low energies but becomes heavily damped at higher energies and can be modeled using a quadratic dispersion. We determined a spin wave stiffness constant of D=94±3 meV Å2. Assuming a nearest-neighbor Heisenberg model we find reasonable agreement between the exchange determined from D and the bulk Curie temperature. Several possible mechanisms to account for the observed spin-wave damping are discussed. © 2010 The American Physical Society.

Abstract:

We investigate the structures of H(3)Co(CN)(6) and D(3)Co(CN)(6) and their temperature dependence using a combination of advanced neutron and x-ray diffraction techniques. Lattice parameter refinements show marked temperature- and isotope-dependent effects in the thermal expansion behaviour. Reverse Monte Carlo modelling of neutron total scattering data characterizes the distribution of D atom positions in the deuterated compound; analysis of these distributions reveals that the two N-H/D bonds become increasingly different with increasing temperature, suggesting a mechanism for the observed thermal expansion anomalies. We discuss these results in the context of the previous crystallographic, spectroscopic and theoretical results for H(3)Co(CN)(6) and 'super-short' N···H···N systems in general.