  By means of neutron scattering techniques we have investigated the frustrated
pyrochlore magnet Ho_2Sn_2O_7, which was found to show a ferromagnetic spin-ice
behavior below T \simeq 1.4 K by susceptibility measurements. High-resolution
powder-neutron-diffraction shows no detectable disorder of the lattice, which
implies appearance of a random magnetic state solely by frustrated geometry,
i.e., the corner sharing tetrahedra. Magnetic inelastic-scattering spectra show
that Ho magnetic moments behave as an Ising spin system at low temperatures,
and that the spin fluctuation has static character. The system remains in a
short-range ordered state down to T = 0.4 K. By analyzing the wave-number
dependence of the magnetic scattering using a mean field theory, it is
clarified that the Ising spins interact via the dipolar interaction. Therefore
we conclude that Ho_2Sn_2O_7 belongs to the dipolar-spin-ice family. Slow spin
dynamics is exhibited as thermal hysteresis and time dependence of the magnetic
scattering.
