Magnetic Coulomb phase in the spin ice Ho2Ti2O7

Magnetic Monopoles Magnets come with a north and a south pole. Despite being predicted to exist, searches in astronomy and in high-energy particle physics experiments for magnetic monopoles (either north or south on their own) have defied observation. Theoretical work in condensed-matter systems has predicted that spin-ice structures may harbor such elusive particles (see the Perspective by Gingras ). Fennell et al. (p. 415 , published online 3 September) and Morris et al. (p. 411 , published online 3 September) used polarized neutron scattering to probe the spin structure forming in two spin-ice compounds—Ho 2 Ti 2 O 7 and Dy 2 Ti 2 O 7 —and present results in support of the presence of magnetic monopoles in both materials.