Abstract
We present here temperature-dependent Raman, x-ray diffraction, and specific heat studies between room temperature and 12 K on single crystals of spin-ice pyrochlore compound and its nonmagnetic analog . Raman data show a “new” band not predicted by factor group analysis of Raman-active modes for the pyrochlore structure in , appearing below a temperature of with a concomitant contraction of the cubic unit cell volume as determined from the powder x-ray diffraction analysis. Low-temperature Raman experiments on -isotope substituted confirm the phonon origin of the new mode. These findings, absent in , suggest that the room-temperature cubic lattice of the pyrochlore undergoes a “subtle” structural transformation near . We find anomalous redshift of some of the phonon modes in both the and the as the temperature decreases, which is attributed to strong phonon-phonon anharmonic interactions.
2 More- Received 9 July 2008
DOI:https://doi.org/10.1103/PhysRevB.78.214102
©2008 American Physical Society