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.

We report on the magnetic excitation spectrum in the normal state of the heavy-fermion superconductor ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ on approaching the quantum critical point (QCP). The magnetic response in the superconducting state is characterized by a transfer of spectral weight to energies above a spin excitation gap. In the normal state, a slowing-down of the quasielastic magnetic response is observed, which conforms to the scaling expected for a QCP of spin-density-wave type. This interpretation is substantiated by an analysis of specific heat data and the momentum dependence of the magnetic excitation spectrum. Our study represents the first direct observation of an almost critical slowing-down of the normal state magnetic response at a QCP when suppressing superconductivity. The results strongly imply that the coupling of Cooper pairs in ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ is mediated by overdamped spin fluctuations.

The chiral components in the magnetic order in multiferroic MnWO4 have been studied by neutron diffraction using spherical polarization analysis as a function of temperature and of external electric field. We show that sufficiently close to the ferroelectric transition at T=12.3$\hskip0.3em${}K it is possible to switch the chiral component by applying moderate electric fields at constant temperature. Full hysteresis cycles can be observed which indicate strong pinning of the magnetic order. MnWO4, furthermore, exhibits a magnetoelectric memory effect across heating into the paramagnetic and paraelectric phase.