X-ray and neutron scattering

Abstract:

Photo-excitation in complex oxides1 transfers charge across semicovalent bonds, drastically perturbing spin and orbital orders2. Light may then be used in compounds like magnetoresistive manganites to control magnetism on nanometre lengthscales and ultrafast timescales. Here, we show how ultrafast resonant soft x-ray diffraction can separately probe the photo-induced dynamics of spin and orbital orders in La0.5Sr1.5MnO4. Ultrafast melting of CE antiferromagnetic spin order is evidenced by the disappearance of a (1/4,1/4,1/2) diffraction peak. On the other hand the (1/4,1/4,0) peak, reflecting orbital order, is only partially reduced. Cluster calculations aid our interpretation by considering different magnetically ordered states accessible after photo-excitation. Nonthermal coupling between light and magnetism emerges as a primary aspect of photo-induced phase transitions in manganites.

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.