Long-Range Order in the Dipolar $XY$ Antiferromagnet Er$_2$Sn$_2$O$_7$

S. Petit 1 E. Lhotel 2 F. Damay 1 P. Boutrouille 1 A. Forget 3 D. Colson 3
3 LNO - Laboratoire Nano-Magnétisme et Oxydes
SPEC - UMR3680 - Service de physique de l'état condensé, IRAMIS - Institut Rayonnement Matière de Saclay
Abstract : 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.
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Physical Review Letters, American Physical Society, 2017, 119, pp.187202. 〈10.1103/PhysRevLett.119.187202〉
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S. Petit, E. Lhotel, F. Damay, P. Boutrouille, A. Forget, et al.. Long-Range Order in the Dipolar $XY$ Antiferromagnet Er$_2$Sn$_2$O$_7$. Physical Review Letters, American Physical Society, 2017, 119, pp.187202. 〈10.1103/PhysRevLett.119.187202〉. 〈cea-01633911〉

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