${\text{Gd}}_2{\text{Sn}}_2{\text{O}}_7$ is believed to be a good approximation to a Heisenberg antiferromagnet on a pyrochlore lattice with exchange and dipole-dipole interactions. The system is known to enter a long-range ordered ground state (the “Palmer Chalker” state) below $T_c=1\text{K}$ with ${\mathit{k}}_{\text{ord}}=\left(000\right)$. However, persistent electronic spin fluctuations have been observed as $T\to 0$. Using inelastic neutron scattering, we have studied the buildup of short-range spin-spin correlations as the temperature is lowered, and the eventual formation of a gapped long-range ordered state that is able to sustain spin waves below $T_c$. As a magnetic field is applied, new magnetic phases develop and the gap widens. These measurements show that ${\text{Gd}}_2{\text{Sn}}_2{\text{O}}_7$ completely relieves itself of frustration, but the self-selected ground state is very delicate.

• Received 1 October 2008

DOI:https://doi.org/10.1103/PhysRevB.78.132410