X-ray and neutron scattering

Abstract:

A birefringence imaging microscopy study of LiTaO3 and some mixed LiTa x Nb1-x O3 crystals is reported. The initially congruent LiTaO3 crystals have been subject to vapour transport equilibration in order to increase the Li content and at the same time to reduce the optical birefringence close to zero at room temperature. In both types of crystal, the presence of unusual periodic self-organized stripes, existing over large distances, has been observed, which correlate with the well documented cleavage and twin planes in this material. Furthermore, the stripes become narrower as the temperature is changed away from the zero-birefringence temperature, but become temperature-independent above the ferroelectric- paraelectric phase-transition temperature. © 2010 International Union of Crystallography Printed in Singapore-all rights reserved.

Abstract:

We present ultrafast resonant soft-x-ray diffraction measurements of time-dependent orbital order in the single-layer-manganite La0.5Sr1.5MnO4. These experiments reveal the appearance of a metastable phase with reduced ordering, different from any thermal state of the system. © OSA / UP 2010.

Abstract:

We report measurements of the magnetic excitation spectrum of the layered antiferromagnet La2 CoO4 by time-of-flight neutron inelastic scattering. In the energy range probed in our experiments (0-250 meV) the magnetic spectrum consists of spin-wave modes with strong in-plane dispersion extending up to 60 meV, and a nearly dispersionless peak at 190 meV. The spin-wave modes exhibit a small (∼1meV) dispersion along the magnetic zone boundary. We show that the magnetic spectrum can be described very well by a model of a Heisenberg antiferromagnet that includes the full spin and orbital degrees of freedom of Co2⊃+ in an axially distorted crystal field. The collective magnetic dynamics are found to be controlled by dominant nearest-neighbor exchange interactions, strong XY-like single-ion anisotropy and a substantial unquenched orbital angular momentum. © 2010 The American Physical Society.

Abstract:

We present data on the magnetic and magnetoelastic coupling in the hexagonal multiferroic manganite LuMnO3 from inelastic neutron scattering, magnetization, and thermal-expansion measurements. We measured the magnon dispersion along the main symmetry directions and used this data to determine the principal exchange parameters from a spin-wave model. An analysis of the magnetic anisotropy in terms of the crystal field acting on the Mn is presented. We compare the results for LuMnO3 with data on other hexagonal R MnO3 compounds. © 2010 The American Physical Society.