Strong spin-phonon coupling in the geometrically frustrated pyrochloreY2Ru2O7

Abstract

We investigated temperature-dependent infrared-active transverse phonon modes of geometrically frustrated pyrochlore ${\mathrm{Y}}_{2}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$, which exhibits a spin-glass-like transition at ${T}_{G}\ensuremath{\sim}80\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. According to previous neutron-scattering experiments, although ${\mathrm{Y}}_{2}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$ does not accompany any static lattice symmetry change, it has an intriguing magnetic ground state with strong antiferromagnetic correlation [M. Ito et al., J. Phys. Soc. Jpn. 69, 888 (2000)]. In our far-infrared spectra, we found seven phonon modes; thermal effects could explain the temperature dependences of three phonons, but not the other four phonons. We found that these abnormal temperature-dependent behaviors could be attributed to a strong antiferromagnetic correlation, not to a structural distortion. Using quantitative analysis, we suggested that the strong spin-phonon coupling effects should play an important role in the intriguing magnetic state of this geometrically frustrated compound.