Neutron scattering study of dipolar spin iceHo2Sn2O7: Frustrated pyrochlore magnet

By means of neutron scattering techniques we have investigated the frustrated pyrochlore magnet ${\mathrm{Ho}}_2{\mathrm{Sn}}_2{\mathrm{O}}_7,$ which was found to show ferromagnetic spin-ice behavior below $T\simeq 1.4\hspace{0.5em}\mathrm{K}$ by susceptibility measurements. High-resolution powder neutron diffraction shows no detectable disorder of the lattice, which implies the 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 at least $T=0.4\mathrm{}\hspace{0.5em}\mathrm{K}.$ By analyzing the wave-vector dependence of the magnetic scattering using a mean-field theory, it is shown that the Ising spins interact via the dipolar interaction. Therefore we conclude that ${\mathrm{Ho}}_2{\mathrm{Sn}}_2{\mathrm{O}}_7$ belongs to the dipolar-spin-ice family. Slow spin dynamics is exhibited as thermal hysteresis and time dependence of the magnetic scattering.