Experimental Proof of a Magnetic Coulomb Phase

Spin ice materials are magnetic substances in which the spin directions map onto hydrogen positions in water ice. Recently this analogy has been elevated to an electromagnetic equivalence, indicating that the spin ice state is a Coulomb phase, with magnetic monopole excitations analogous to ice's mobile ionic defects. No Coulomb phase has yet been proved in a real magnetic material, as the key experimental signature is difficult to resolve in most systems. Here we measure the scattering of polarised neutrons from the prototypical spin ice Ho2Ti2O7. This enables us to separate different contributions to the magnetic correlations to clearly demonstrate the existence of an almost perfect Coulomb phase in this material. The temperature dependence of the scattering is consistent with the existence of deconfined magnetic monopoles connected by Dirac strings of divergent length.Comment: 18 pages, 4 fig

Magnetic Excitations in the Ground State of Yb2Ti2O7\mathrm{Yb_2Ti_2O_7}

We report an extensive study on the zero field ground state of a powder sample of the pyrochlore $\mathrm{Yb_2Ti_2O_7}$. A sharp heat capacity anomaly that labels a low temperature phase transition in this material is observed at 280 mK. Neutron diffraction shows that a \emph{quasi-collinear} ferromagnetic order develops below $T_\mathrm{c}$ with a magnetic moment of $0.87(2)\mu_\mathrm{B}$. High resolution inelastic neutron scattering measurements show, below the phase transition temperature, sharp gapped low-lying magnetic excitations coexisting with a remnant quasielastic contribution likely associated with persistent spin fluctuations. Moreover, a broad inelastic continuum of excitations at $\sim0.6$ meV is observed from the lowest measured temperature up to at least 2.5 K. At 10 K, the continuum has vanished and a broad quasielastic conventional paramagnetic scattering takes place at the observed energy range. Finally, we show that the exchange parameters obtained within the framework of linear spin-wave theory do not accurately describe the observed zero field inelastic neutron scattering data.Comment: 11 pages, 9 figures, Phys. Rev. B. (accepted

Polarization analysis for the thermal chopper spectrometer TOPAS

© 2015 Owned by the authors, published by EDP Sciences. We report on the progress of the construction of the thermal time-of-flight spectrometer with polarization analysis TOPAS at the Mayer-Leibnitz Zentrum (MLZ). The instrument components approach the status to be ready for installation. The special feature of the instrument is its capability for wide-angle polarization analysis in the thermal spectral range. Here we describe a novel approach to rotate the neutron spin adiabatically into the X, Y or Z direction of the laboratory frame by combination of permanent magnets aligned as Halbach rings and electrically generated fields. Despite the severe spatial restrictions the design exhibits a very high adiabaticity and interacts only weakly with the coil layout for the analyzing 3He spin filter cell (SFC)

Can Healthcare Assistant Training (CHAT) improve the relational care of older people? Study protocol for a pilot cluster-randomised controlled trial

Background People aged 75 years and over account for one in four of all hospital admissions. There has been increasing recognition of problems in the care of older people, particularly in hospitals. Evidence suggests that older people judge the care they receive in terms of kindness, empathy, compassion, respectful communication and being seen as a person not just a patient. These are aspects of care to which we refer when we use the term 'relational care'. Healthcare assistants deliver an increasing proportion of direct care to older people, yet their training needs are often overlooked. Methods/design This study will determine the acceptability and feasibility of a cluster randomised controlled trial of 'Older People's Shoes' a two-day training intervention for healthcare assistants caring for older people in hospital. Within this pilot, two-arm, parallel, cluster randomised controlled trial, healthcare assistants within acute hospital wards are randomised to either the two-day training intervention or training as usual. Registered nurses deliver 'Older People's Shoes' over two days, approximately one week apart. It contains three components: experiential learning about ageing, exploration of older people's stories, and customer care. Outcomes will be measured at the level of patient (experience of emotional care and quality of life during their hospital stay), healthcare assistant (empathy and attitudes towards older people), and ward (quality of staff/patient interaction). Semi-structured interviews of a purposive sample of healthcare assistants receiving the intervention, and all trainers delivering the intervention, will be undertaken to gain insights into the experiences of both the intervention and the trial, and its perceived impact on practice. Trial registration The study was registered as an International Standard Randomised Contolled Trial (ISRCTN10385799) on 29 December 2014

Neutron scattering studies of frustrated magnets

Here is presented an experimental study of the low-temperature magnetic behaviour of the spin ice holmium titanate, Ho_2Ti_2O_7; stuffed spin ice, Ho_{2+x}Ti_{2-x}O_{7-x/2}; and neodymium zirconate, Nd_2Zr_2O_7. The main techniques utilised here are based on neutron scattering which gives information on the static and dynamic behaviour of materials. Stuffed spin ice represents the addition of holmium magnetic moments into holmium titanate. This addition of the Ho^3^+ affects the oxygen lattice which is responsible for the considerable magnetocrystalline anisotropy in these materials. Inelastic scattering measurements reveal that a crystal of Ho_{2.3}Ti_{1.7}O_{6.85} is a static magnetic system at the lowest energies. Elastic neutron scattering on the same crystal reveals short-range order that distinguishes it from spin ice. Neodymium zirconate, Nd_2Zr_2O_7, is a stoichiometric pyrochlore material isomorphous to holmium titanate in structure. Here a single crystal and a powder sample have been investigated by both elastic and inelastic scattering. The powder and crystals exhibit low temperature intensity in the same temperature range indicating a low temperature transition which has been shown to be second order. A field induced transition has also been studied, but its origin has not been established. Holmium titanate is a stoichiometric material unlike stuffed spin ice. Here a study has been conducted into scattering in the hhl plane under application of a magnetic field at a temperature of 60 mK. The results indicate a breaking of the ordered \alpha-chain structure within the material as the field is removed

Neutron scattering studies of frustrated magnets.

Here is presented an experimental study of the low-temperature magnetic behaviour of the spin ice holmium titanate, Ho_2Ti_2O_7; stuffed spin ice, Ho_{2+x}Ti_{2-x}O_{7-x/2}; and neodymium zirconate, Nd_2Zr_2O_7. The main techniques utilised here are based on neutron scattering which gives information on the static and dynamic behaviour of materials. Stuffed spin ice represents the addition of holmium magnetic moments into holmium titanate. This addition of the Ho^3^+ affects the oxygen lattice which is responsible for the considerable magnetocrystalline anisotropy in these materials. Inelastic scattering measurements reveal that a crystal of Ho_{2.3}Ti_{1.7}O_{6.85} is a static magnetic system at the lowest energies. Elastic neutron scattering on the same crystal reveals short-range order that distinguishes it from spin ice. Neodymium zirconate, Nd_2Zr_2O_7, is a stoichiometric pyrochlore material isomorphous to holmium titanate in structure. Here a single crystal and a powder sample have been investigated by both elastic and inelastic scattering. The powder and crystals exhibit low temperature intensity in the same temperature range indicating a low temperature transition which has been shown to be second order. A field induced transition has also been studied, but its origin has not been established. Holmium titanate is a stoichiometric material unlike stuffed spin ice. Here a study has been conducted into scattering in the hhl plane under application of a magnetic field at a temperature of 60 mK. The results indicate a breaking of the ordered \alpha-chain structure within the material as the field is removed.

Polarization analysis for the thermal chopper spectrometer TOPAS

© 2015 Owned by the authors, published by EDP Sciences. We report on the progress of the construction of the thermal time-of-flight spectrometer with polarization analysis TOPAS at the Mayer-Leibnitz Zentrum (MLZ). The instrument components approach the status to be ready for installation. The special feature of the instrument is its capability for wide-angle polarization analysis in the thermal spectral range. Here we describe a novel approach to rotate the neutron spin adiabatically into the X, Y or Z direction of the laboratory frame by combination of permanent magnets aligned as Halbach rings and electrically generated fields. Despite the severe spatial restrictions the design exhibits a very high adiabaticity and interacts only weakly with the coil layout for the analyzing 3He spin filter cell (SFC)

Polarization analysis for the thermal chopper spectrometer TOPAS

© 2015 Owned by the authors, published by EDP Sciences. We report on the progress of the construction of the thermal time-of-flight spectrometer with polarization analysis TOPAS at the Mayer-Leibnitz Zentrum (MLZ). The instrument components approach the status to be ready for installation. The special feature of the instrument is its capability for wide-angle polarization analysis in the thermal spectral range. Here we describe a novel approach to rotate the neutron spin adiabatically into the X, Y or Z direction of the laboratory frame by combination of permanent magnets aligned as Halbach rings and electrically generated fields. Despite the severe spatial restrictions the design exhibits a very high adiabaticity and interacts only weakly with the coil layout for the analyzing 3He spin filter cell (SFC)

Polarization analysis for the thermal chopper spectrometer TOPAS

© 2015 Owned by the authors, published by EDP Sciences. We report on the progress of the construction of the thermal time-of-flight spectrometer with polarization analysis TOPAS at the Mayer-Leibnitz Zentrum (MLZ). The instrument components approach the status to be ready for installation. The special feature of the instrument is its capability for wide-angle polarization analysis in the thermal spectral range. Here we describe a novel approach to rotate the neutron spin adiabatically into the X, Y or Z direction of the laboratory frame by combination of permanent magnets aligned as Halbach rings and electrically generated fields. Despite the severe spatial restrictions the design exhibits a very high adiabaticity and interacts only weakly with the coil layout for the analyzing 3He spin filter cell (SFC)