Palmer-Chalker correlations in the XY pyrochlore antiferromagnet Er2Sn2O7

Er2Sn2O7 is considered, together with Er2Ti2O7, as a realization of the XY antiferromagnet on the pyrochlore lattice. We present magnetization measurements confirming that Er2Sn2O7 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 Er3+ 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 Er2Sn2O7 parameters confirm the role of the latter interactions on top of relatively weak and isotropic exchange couplings.