Palmer-Chalker correlations in the X Y pyrochlore antiferromagnet Er 2 Sn 2 O 7

Er${}_{2}$Sn${}_{2}$O${}_{7}$ is considered, together with Er${}_{2}$Ti${}_{2}$O${}_{7}$, as a realization of the $XY$ antiferromagnet on the pyrochlore lattice. We present magnetization measurements confirming that Er${}_{2}$Sn${}_{2}$O${}_{7}$ does not order down to 100 mK but exhibits a freezing below 200 mK. Our neutron scattering experiments evidence the strong $XY$ character of the Er${}^{3+}$moment and point out the existence of short-range correlations in which the magnetic moments are in peculiar configurations, the Palmer-Chalker states, predicted theoretically for an $XY$ pyrochlore antiferromagnet with dipolar interactions. Our estimation of the Er${}_{2}$Sn${}_{2}$O${}_{7}$ parameters confirm the role of the latter interactions on top of relatively weak and isotropic exchange couplings.