Abstract
In this article, we report negative thermal expansion and spin frustration in hexagonal . Rietveld refinements of the x-ray diffraction patterns reveal that the negative thermal expansion in the temperature range of 50–100 K stems from the triangular lattice of ions. The downward deviation of the low-temperature inverse susceptibility versus plot from the Curie-Weiss law and the large value of the ratio, , where and are respectively Curie-Weiss and Neel temperature, indicate a strong spin frustration, which inhibits long-range magnetic ordering down to 1.8 K. Magnetostriction measurements clearly demonstrate a spin-lattice coupling in the system. Low-temperature anomalous phonon softening, as obtained from temperature-dependent Raman measurements, also reveals the same. Our experimental observations are supported by first-principles density functional theory calculations of the electronic and phonon dispersion in . The calculations suggest that the lattice is highly frustrated at low temperature. Further, the calculated normal mode frequencies of the Gd-related point phonon modes reveal significant magnetoelastic coupling in this system. The competitive role of magnetic interaction energy and thermal stabilization energy in determining the change in interatomic distances is the possible origin for the negative thermal expansion in over a limited range of temperature.
4 More- Received 20 August 2016
- Revised 16 January 2017
DOI:https://doi.org/10.1103/PhysRevB.95.054103
©2017 American Physical Society