Magnetic ordering and dynamics in the XY pyrochlore antiferromagnet: a muon-spin relaxation studyof Er2Ti2O7 and Er2Sn2O7

Abstract

Spin dynamics in Er2Ti2O7 and Er2Sn2O7 have been probed by means of muon-spin relaxation(μ+SR) in the temperature range K. Both compounds are thought to constitute experimental realizationsof the highly frustrated XY antiferromagnet on the pyrochlore lattice, forwhich theory predicts fluctuation-induced magnetic order. Our results forEr2Ti2O7 are consistent with a transition into an ordered state at K, in agreement with previous neutron measurements. Below this temperature, the muon relaxationrate λ(T) remains large ( MHz) and temperature independent, in contrast to the behaviour in conventional magnets. The thermalevolution of λ(T) for Er2Sn2O7 is somewhat similar to that of the Ti material. However, the depolarization curves remainexponential over the entire temperature range, suggesting a dense distribution of rapidly fluctuatingmagnetic moments, and, thus, are compatible with the absence of long-range order at least forT>0.02 K.