Magnetic field dependence of muon spin relaxation in geometrically frustrated Gd2Ti2O7

Muon spin relaxation has been investigated in the geometrically frustrated antiferromagnet Gd2Ti2O7 as a function of magnetic field and temperature. Well above the magnetic ordering temperature of Tc=1K, the field dependence of the muon spin relaxation rate (T1−1) originates from field-induced changes in the spectral density of Gd fluctuations. This allows one to determine both the autocorrelation time and magnitude of the fluctuating local magnetic field at the muon. Well below Tc a coherent precession signal is observed, corresponding to a much smaller quasistatic local magnetic field. At low temperatures T1−1 levels off, at a constant value which is much larger than reported recently for a single crystal of Gd2Ti2O7 [Yaouanc , Phys. Rev. Lett. 95, 047203 (2005)]. A magnetic field of 2T completely quenches the low-temperature spin relaxation in the present sample. These results indicate that the ordered state is characterized by low-frequency dynamics which are most likely due to residual crystalline disorder.