μSR investigation of spin dynamics in the spin-ice material Dy₂Ti₂O₇

Abstract

We present a detailed muon spin relaxation (<em>μ</em>⁺SR) study of the spin-ice material Dy₂Ti₂O₇. Polycrystalline samples of this material have been studied in the temperature range 0.02 K &lt; <em>T</em> &lt; 300 K in applied longitudinal magnetic fields of up to 2.7 T. At high temperature our study confirms previous bulk results showing that dynamics are dominated by spin-phonon-mediated relaxation of the electronic spin system. Below about 60 K the depolarization of the muon ensemble becomes too fast and the signal is almost completely lost. However, the recovery at lower temperature of the resolved asymmetry to roughly 1/3 of the total value allows us to confirm that it is the development of strong quasi-static local fields and not only dynamical effects that causes this depolarization. Finally, we find evidence of remanent spin fluctuations at temperatures as low as 0.02 K, well inside the quenched spin-ice state. We tentatively ascribe these to the hyperfine interaction with the ¹⁶¹Dy and ¹⁶³Dy nuclear spins.