X-ray and neutron scattering

Abstract:

We report the complex refractive index of La5/3Sr1/3NiO4 over the terahertz frequency range, obtained using time-domain spectroscopy. Negligible change in the complex refractive index with magnetic flux densities up to 6T was seen, while changes were observed as the lattice temperature was increased from 1.5 K to the charge-ordering temperature at 220 K. The terahertz frequency response therefore originates from the dielectric function rather than the magnetic permeability.

Abstract:

We explore the possibility that detailed dynamical information might be extracted from powder diffraction data. Our focus is a recently reported technique that employs statistical analysis of atomistic configurations to calculate dynamical properties from neutron total scattering data. We show that it is possible to access the phonon dispersion of low-frequency modes using such an approach, without constraining the results in terms of some pre-defined dynamical model. The high-frequency regions of the phonon spectrum are found to be less well preserved in the diffraction data. © 2006.

Abstract:

The magnetic ground state of a single crystalline bilayered manganite La1.1 Sr1.9 Mn2 O7 is investigated using bulk magnetic measurements. Besides large relaxation times, memory effects reminiscent of that seen in spin glasses are also observed both in the field cooled and zero field cooled measurement protocols. These indicate that this system is not a canted antiferromagnet as was reported earlier, but on the contrary has an inhomogenous magnetic ground state arising as a consequence of phase separation. We also report the observation of sharp metamagnetic steps in this bilayered manganite, similar to that seen in phase separated three-dimensional perovskites. © 2006 The American Physical Society.