  We report measurements performed on a polycrystalline sample of the
pyrochlore compound Nd2Sn2O7. It undergoes a second order magnetic phase
transition at Tc ~ 0.91 K to a noncoplanar all-in-all-out magnetic structure of
the Nd3+ magnetic moments. The thermal behavior of the low temperature specific
heat fingerprints excitations with linear dispersion in a three-dimensional
lattice. The temperature independent spin-lattice relaxation rate measured
below Tc and the anomalously slow paramagnetic spin dynamics detected up to ~
30 Tc are suggested to be due to magnetic short-range correlations in
unidimensional spin clusters, i.e., spin loops. The observation of a
spontaneous field in muon spin relaxation measurements is associated with the
absence of a divergence-free field for the ground state of an all-in-all-out
pyrochlore magnet as predicted recently.
