Optical phonons, spin correlations, and spin-phonon coupling in the frustrated pyrochlore magnets CdCr2O4 and ZnCr2O4

Abstract

We report on infrared, Raman, magnetic susceptibility, and specific heat measurements on CdCr2O4 and ZnCr2O4 single crystals. We estimate the nearest-neighbor and next-nearest neighbor exchange constants from the magnetic susceptibility and extract the spin-spin correlation functions obtained from the magnetic susceptibility and the magnetic contribution to the specific heat. By comparing with the frequency shift of the infrared optical phonons above TN , we derive estimates for the spin-phonon coupling constants in these systems. The observation of phonon modes which are both Raman and infrared active suggest the loss of inversion symmetry below the Neel temperature in CdCr2O4 in agreement with theoretical predictions by Chern and coworkers [Phys. Rev. B 74, 060405 (2006)]. In ZnCr2O4 several new modes appear below TN, but no phonon modes could be detected which are both Raman and infrared active indicating the conservation of inversion symmetry in the low temperature phase.

11 pages, 13 figures

References in corpus (6)

• Magnetic-induced phonon anisotropy in ZnCr${}_2$O${}_4$ from first principles
• Spin-phonon coupling in antiferromagnetic chromium spinels
• Broken parity and a chiral ground state in the frustrated magnet CdCr2O4
• Spin phonon coupling in frustrated magnet CdCr${}_2$O${}_4$
• Optical properties of ZnCr2Se4 - Spin-phonon coupling and electronic d-d-like excitations
• Evidence for orthorhombic distortions in the ordered state of ZnCr${}_2$O${}_4$: A magnetic resonance study

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