Strong spin-phonon coupling in the geometrically frustrated pyrochlore Y₂Ru₂O₇

We investigated temperature-dependent infrared-active transverse phonon modes of geometrically frustrated pyrochlore Y₂Ru₂O ₇, which exhibits a spin-glass-like transition at T _G∼80 K. According to previous neutron-scattering experiments, although Y₂Ru₂O₇ 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.