3. April 2018

Dipolar Spin Ice States with a Fast Monopole Hopping Rate in CdEr₂X₄ (X = Se, S)

S. Gao et al., Physical Review Letters 120, 137201 (2018). Excitations in a spin ice behave as magnetic monopoles, and their population and mobility control the dynamics of a spin ice at low temperature. CdEr₂Se₄ is reported to have the Pauling entropy characteristic of a spin ice, but its dynamics are three orders of magnitude faster than the canonical spin ice Dy₂Ti₂O₇. In this Letter we use diffuse neutron scattering to show that both CdEr₂Se₄ and CdEr₂S₄ support a dipolar spin ice state—the host phase for a Coulomb gas of emergent magnetic monopoles. These Coulomb gases have similar parameters to those in Dy₂Ti₂O₇, i.e., dilute and uncorrelated, and so cannot provide three orders faster dynamics through a larger monopole population alone. We investigate the monopole dynamics using ac susceptometry and neutron spin echo spectroscopy, and verify the crystal electric field Hamiltonian of the Er³⁺ ions using inelastic neutron scattering. A quantitative calculation of the monopole hopping rate using our Coulomb gas and crystal electric field parameters shows that the fast dynamics in CdEr₂X₄ (X = Se, S) are primarily due to much faster monopole hopping. Our work suggests that CdEr₂X₄ offer the possibility to study alternative spin ice ground states and dynamics, with equilibration possible at much lower temperatures than the rare earth pyrochlore examples.

12. February 2018

Imaging at Paul Scherrer Institute helps to increase production at ABB site in Aargau

The ABB facility in Wettingen, Aargau, got practical recommendations on increasing output in the manufacture of ceramic components. The ceramics in question are voltage-dependent resistors used in overvoltage protectors – a kind of lightning protection system – for example in electrical transmission lines. Researchers of the Laboratory for Neutron Scattering and Imaging at the Paul Scherrer Institute PSI examined the components by means of neutron imaging. With the help of these images, ABB employees were able to see where there was potential for further process optimisation. This investigation took place within the framework of a feasibility study funded by Hightech Zentrum Aargau. PSI Media Release

11. December 2017

SwedNess Students visit PSI for hands-on training in neutron scattering

To take full advantage of the upcoming European Spallation Source facility ESS, strategic funding has been allocated to rebuild and expand the Swedish neutron scattering community. One of the most important actions is the establishment of the Swedish national graduate school in neutron scattering (SwedNess). Up to 40 PhD students will be fully funded, employed and trained within this school. In the end of September 2017, the first 20 PhD students arrived at the Paul Scherrer Institute (PSI) and the Swiss Spallation Neutron Source (SINQ) for their very first hands-on training in neutron scattering. During their week at PSI the SwedNess students obtained specific training in neutron reflectometry as well as neutron and x-ray imaging. The training was very much appreciated by the students and PSI looks forward to welcoming them back in a near future as scientific users of the SINQ neutron facility.

15. November 2017

Spin Resonance and Magnetic Order in an Unconventional Superconductor

D.G. Mazzone et al., Physical Review Letters 119, 187002 (2017). Unconventional superconductivity in many materials is believed to be mediated by magnetic fluctuations. It is an open question how magnetic order can emerge from a superconducting condensate and how it competes with the magnetic spin resonance in unconventional superconductors. Here we study a model d-wave superconductor that develops spin-density wave order, and find that the spin resonance is unaffected by the onset of static magnetic order. This result suggests a scenario, in which the resonance in Nd_0.05Ce_0.95CoIn₅ is a longitudinal mode with fluctuating moments along the ordered magnetic moments.