Absence of strong magnetic fluctuations in the iron phosphide superconductors LaFePO and Sr2ScO3FeP

We report neutron inelastic scattering measurements on polycrystalline LaFePO and Sr2ScO3FeP, two members of the iron phosphide families of superconductors. No evidence is found for any magnetic fluctuations in the spectrum of either material in the energy and wavevector ranges probed. Special attention is paid to the wavevector at which spin-density-wave-like fluctuations are seen in other iron-based superconductors. We estimate that the magnetic signal, if present, is at least a factor of four (Sr2ScO3FeP) or seven (LaFePO) smaller than in the related iron arsenide and chalcogenide superconductors. These results suggest that magnetic fluctuations are not as influential on the electronic properties of the iron phosphide systems as they are in other iron-based superconductors.Comment: 7 pages, 5 figure

Spin resonance in the superconducting state of Li1−x_{1-x}Fex_{x}ODFe1−y_{1-y}Se observed by neutron spectroscopy

We have performed inelastic neutron scattering measurements on a powder sample of the superconductor lithium iron selenide hydroxide Li$_{1-x}$Fe$_{x}$ODFe$_{1-y}$Se ($x \simeq 0.16, y \simeq 0.02$, $T_{\rm c} = 41$\,K). The spectrum shows an enhanced intensity below $T_{\rm c}$ over an energy range $0.64\times2\Delta < E < 2\Delta$, where $\Delta$ is the superconducting gap, with maxima at the wave vectors $Q_1 \simeq 1.46$\,\AA$^{-1}$ and $Q_2 \simeq 1.97$\,\AA$^{-1}$. The behavior of this feature is consistent with the spin resonance mode found in other unconventional superconductors, and strongly resembles the spin resonance observed in the spectrum of the molecular-intercalated iron selenide, Li$_{0.6}$(ND$_{2}$)$_{0.2}$(ND$_{3}$)$_{0.8}$Fe$_{2}$Se$_{2}$. The signal can be described with a characteristic two-dimensional wave vector $(\pi, 0.67\pi)$ in the Brillouin zone of the iron square lattice, consistent with the nesting vector between electron Fermi sheets

Incommensurate antiferromagnetic fluctuations in single-crystalline LiFeAs studied by inelastic neutron scattering

We present an inelastic neutron scattering study on single-crystalline LiFeAs devoted to the characterization of the incommensurate antiferromagnetic fluctuations at $\mathbf{Q}=(0.5\pm\delta, 0.5\mp\delta, q_l)$. Time-of-flight measurements show the presence of these magnetic fluctuations up to an energy transfer of 60 meV, while polarized neutrons in combination with longitudinal polarization analysis on a triple-axis spectrometer prove the pure magnetic origin of this signal. The normalization of the magnetic scattering to an absolute scale yields that magnetic fluctuations in LiFeAs are by a factor eight weaker than the resonance signal in nearly optimally Co-doped BaFe$_2$As$_2$, although a factor two is recovered due to the split peaks owing to the incommensurability. The longitudinal polarization analysis indicates weak spin space anisotropy with slightly stronger out-of-plane component between 6 and 12 meV. Furthermore, our data suggest a fine structure of the magnetic signal most likely arising from superposing nesting vectors.Comment: 9 pages, 8 figure

The Final Chapter In The Saga Of YIG

The magnetic insulator Yttrium Iron Garnet can be grown with exceptional quality, has a ferrimagnetic transition temperature of nearly 600 K, and is used in microwave and spintronic devices that can operate at room temperature. The most accurate prior measurements of the magnon spectrum date back nearly 40 years, but cover only 3 of the lowest energy modes out of 20 distinct magnon branches. Here we have used time-of-flight inelastic neutron scattering to measure the full magnon spectrum throughout the Brillouin zone. We find that the existing model of the excitation spectrum, well known from an earlier work titled "The Saga of YIG", fails to describe the optical magnon modes. Using a very general spin Hamiltonian, we show that the magnetic interactions are both longer-ranged and more complex than was previously understood. The results provide the basis for accurate microscopic models of the finite temperature magnetic properties of Yttrium Iron Garnet, necessary for next-generation electronic devices.Comment: 10 pages, 3 figures, 4 supplementary figures, 1 table, 1 supplementary tabl

PP12 New ‘nature of call’ telephone screening tool, employed prior to nhs pathways triage, can accurately identify those later treated for out of hospital cardiac arrest: analysis of sensitivity and specificity using routine ambulance service data

BackgroundA new pre-triage emergency medical call screening tool, Nature of Call (NoC), has been introduced into UK ambulance services which employ the NHS Pathways (NHSP) triage system. Its current function is to provide a rapid sieve, differentiating between patients who may need treatment for Out-of-Hospital Cardiac Arrest (OHCA), and therefore require immediate ambulance dispatch, and all other calls, for which ambulance dispatch is withheld whilst further triage is undertaken.ObjectiveTo evaluate the accuracy of NoC in identifying patients with potentially treatable OHCA or peri-arrest conditions.MethodsStudy of diagnostic accuracy. The sample was a retrospective cohort of consecutive calls to a UK ambulance service, taken over a four-month period. Sensitivity and specificity were determined, comparing allocated priority dispositions with an OHCA Treatment Registry. Context was supplied by the evaluation of subsequent categorisation by NHSP. The accuracy of the combined NoC and NHSP allocations was also investigated.ResultsA total of 1 87 419 emergency calls were received. Of these, 71 373 were allocated both NoC and NHSP priority dispositions and were associated with electronic Patient Clinical Records. 590 (0.8%) of these patients received treatment for OHCA. NoC, sensitivity=77.6% (95% CI 74.1 to 80.8); specificity=86.9% (95% CI 86.6 to 87.1). NHSP, sensitivity=79.2% (95% CI 75.7 to 82.2); specificity=93.4% (93.2 to 93.6). NoC and NHSP combined, sensitivity=84.1% (95% CI 80.9 to 86.8); specificity=95.0% (95% CI 94.8 to 95.3).ConclusionsNoC and subsequent NHSP call categorisation each achieved relatively high sensitivity for the identification of treated OHCA, predicting similar groups of registry patients (although 6% were identified by NoC alone). Overall accuracy was enhanced when NoC and subsequent NHSP Results were combined. The unidentified group of treated OHCA patients (16%) present a challenge to the current dispatch system which relies on the early recognition of patients who may require treatment for OHCA.</jats:sec

PP13 The NHS pathways (NHSP) medical call triage system and new ‘nature of call’ telephone screening tool, employed prior to NHSP, can accurately identify high acuity patients: analysis of sensitivity and specificity using routine ambulance service data

BackgroundThe NHS Pathways (NHSP) medical call triage system is employed by UK ambulance services. One function is to identify a broad category of ‘high-acuity calls’, distinguishing them from those that do not require an emergency response. A new pre-triage screening tool, Nature of Call (NoC), designed to augment NHSP could be employed as a rapid initial sieve of broad acuity.ObjectivesTo identify the accuracy of NHSP (and NoC) in recognising patients who require an emergency ambulance response (and therefore those who may not).MethodsDiagnostic accuracy. The sample is a retrospective cohort of consecutive calls, over a 4 month period, to a UK ambulance service. Sensitivity and specificity were determined, comparing allocated NoC and NHS Pathways priority dispositions with a composite reference standard comprised of administered medications, procedures, observations and clinical impressions associated with high-acuity, as recorded on ambulance electronic Patient Clinical Records.ResultsA total of 1 87 408 emergency calls were received. Of these, 71 373 were allocated both NoC and NHSP priority dispositions and were associated with electronic Patient Clinical Records. 40 997 (57%) of these patients met the high-acuity reference criteria. NHSP, sensitivity=98.1% (95% CI 98.0 to 98.2); specificity=5.9% (95% CI 5.6 to 6.1). NoC, sensitivity=84.0% (95% CI 83.7 to 84.4); specificity=26.5% (95% CI 26.0 to 27.0).ConclusionsNHSP is effective in identifying high-acuity patients (as is NoC). Sensitivity analysis therefore supports the this function of NHSP and NoC/NHSP to inform initial ambulance dispatch decisions, particularly if NoC categorisation is reviewed in the light of subsequent NHSP triage. However, both systems appear to achieve high sensitivity by also allocating most low-acuity calls to high-acuity categories. This significantly restricts operational application. Only one quarter of low-acuity calls are allocated the lowest priority category by NoC and one-in-seventeen by NHSP, severely restricting the group likely to be considered for alternative care pathways.</jats:sec

Accuracy of nature of call screening tool in identifying patients requiring treatment for out of hospital cardiac arrest

BackgroundA new pre-triage screening tool, Nature of Call (NoC), has been introduced into the telephone triage system of UK ambulance services which employ National Health Service Pathways (NHSP). Its function is to provide rapid recognition of patients who may need immediate ambulance dispatch for out-of-hospital cardiac arrest (OHCA) and withholding dispatch for other calls while further triage is undertaken. In this study, we evaluated the accuracy of NoC and NHSP in identifying patients with potentially treatable or imminent OHCA.MethodsThis retrospective, observational study reviewed consecutive calls to a UK ambulance service between October 2016 and February 2017 in which NOC, and then NHSP were applied sequentially. Only those calls for which a corresponding electronic Patient Clinical Record was available were included. Sensitivity and specificity of NOC and NHSP for recognition of an OHCA were determined by comparing allocated priority dispositions with an OHCA Treatment Registry (OHCATR).ResultsOf 96 423 calls received, 71 373 were reviewed. For 590 (0.8%) of these calls, the patients received treatment for OHCA. NOC identified 458 OHCATR patients; NHSP identified 467; together they identified 496. NoC captured 29 patients not identified by NHSP; NHSP captured 38 patients not identified by NOC. For NOC sensitivity was 77.6% (95% CI 74.1 to 80.8) and specificity 86.9% (95% CI 86.6 to 87.1). NHSP sensitivity was 79.2% (95% CI 75.7 to 82.2) and specificity 93.4% (95% CI 93.2 to 93.6). NoC and NHSP combined had a sensitivity of 84.1% (95% CI 80.9 to 86.8) and specificity of 85.3% (95% CI 85.1 to 85.6).ConclusionsNoC and NHSP call categorisation each achieved similar sensitivity for the identification of OHCATR, identifying most of the same patients, but each captured unique patients. Using both methods sequentially improved accuracy. The 16% of OHCATR patients not identified by either method present a challenge to ambulance dispatch systems.</jats:sec