Long-Range Order in the Dipolar XY Antiferromagnet Er2Sn2O7

S. Petit (1) , Elsa Lhotel (2) , F. Damay (1) , P. Boutrouille (1) , A. Forget (3) , D. Colson (3)

1 LLB - UMR 12 - Laboratoire Léon Brillouin
2 NEEL - MagSup - Magnétisme et Supraconductivité
3 LNO - Laboratoire Nano-Magnétisme et Oxydes

Er$_2$Sn$_2$O$_7$ remains a puzzling case among the extensively studied frustrated compounds of the rare-earth pyrochlore family. Indeed, while a first-order transition towards a long-range antiferromagnetic state with the so-called Palmer-Chalker structure is theoretically predicted, it has not yet been observed, leaving the issue as to whether it is a spin-liquid candidate open. We report on neutron scattering and magnetization measurements which evidence a second-order transition towards this Palmer-Chalker ordered state around 108 mK. Extreme care was taken to ensure a proper thermalization of the sample, which has proved to be crucial to successfully observe the magnetic Bragg peaks. At the transition, a gap opens in the excitations, superimposed on a strong quasielastic signal. The exchange parameters, refined from a spin-wave analysis in applied magnetic field, confirm that Er$_2$Sn$_2$O$_7$ is a realization of the dipolar $XY$ pyrochlore antiferromagnet. The proximity of competing phases and the strong $XY$ anisotropy of the Er$^{3+}$ magnetic moment might be at the origin of enhanced fluctuations, leading to the unexpected nature of the transition, the low ordering temperature, and the observed multiscale dynamics.

Domaines: Physique [physics]

S. Petit, Elsa Lhotel, F. Damay, P. Boutrouille, A. Forget, et al.. Long-Range Order in the Dipolar XY Antiferromagnet Er2Sn2O7. Physical Review Letters, 2017, 119 (18), pp.187202. ⟨10.1103/PhysRevLett.119.187202⟩. ⟨cea-01633911⟩