Spin-liquid dynamics of pyrochlore magnets Gd2Ti2O7 and Gd2Sn2O7

TL;DR

This study investigates the spin-liquid phase of Gd2Ti2O7 and Gd2Sn2O7 pyrochlore magnets using electron spin resonance, revealing gapped excitations and collective spin modes that emerge above the magnetic ordering temperature.

Contribution

It provides the first ESR evidence of gapped excitations and collective spin modes in the spin-liquid phase of these pyrochlore magnets.

Findings

Gaps in excitation spectra open below Curie-Weiss temperature.

Gaps increase linearly with external magnetic field.

Gd2Ti2O7 exhibits an additional paramagnetic line.

Abstract

The spin-liquid phase of two highly frustrated pyrochlore magnets Gd2Ti2O7 and Gd2Sn2O7 is probed using electron spin resonance in the temperature range 1.3 - 30 K. The deviation of the absorption line from the paramagnetic position \nu =\gamma H observed in both compounds below the Curie-Weiss temperature \Theta_CW ~ 10 K, suggests an opening up of a gap in the excitation spectra. On cooling to 1.3 K (which is above the ordering transition T_N ~ 1.0 K) the resonance spectrum is transformed into a wide band of excitations with the gap amounting to \Delta ~ 26 GHz (1.2 K) in Gd2Ti2O7 and 18 GHz (0.8 K) in Gd2Sn2O7. The gaps increase linearly with the external magnetic field. For Gd2Ti2O7 this branch co-exists with an additional nearly paramagnetic line absent in Gd2Sn2O7. These low lying excitations with gaps, which are preformed in the spin-liquid state, may be interpreted as collective spin modes split by the single-ion anisotropy.