Resonant photon absorption and hole burning in Cr7Ni antiferromagnetic rings

Presented are magnetization measurements on a crystal of Cr7Ni antiferromagnetic rings. Irradiation with microwaves at frequencies between 1 and 10 GHz leads to observation of very narrow resonant photon absorption lines which are mainly broadened by hyperfin interactions. A two-pulse hole burning technique allowed us to estimate the characteristic energy diffusion time.Comment: 4 pages, 5 figure

Low temperature magnetization and the excitation spectrum of antiferromagnetic Heisenberg spin rings

Accurate results are obtained for the low temperature magnetization versus magnetic field of Heisenberg spin rings consisting of an even number N of intrinsic spins s = 1/2, 1, 3/2, 2, 5/2, 3, 7/2 with nearest-neighbor antiferromagnetic (AF) exchange by employing a numerically exact quantum Monte Carlo method. A straightforward analysis of this data, in particular the values of the level-crossing fields, provides accurate results for the lowest energy eigenvalue E(N,S,s) for each value of the total spin quantum number S. In particular, the results are substantially more accurate than those provided by the rotational band approximation. For s <= 5/2, data are presented for all even N <= 20, which are particularly relevant for experiments on finite magnetic rings. Furthermore, we find that for s > 1 the dependence of E(N,S,s) on s can be described by a scaling relation, and this relation is shown to hold well for ring sizes up to N = 80 for all intrinsic spins in the range 3/2 <= s <= 7/2. Considering ring sizes in the interval 8 <= N <= 50, we find that the energy gap between the ground state and the first excited state approaches zero proportional to 1/N^a, where a = 0.76 for s = 3/2 and a = 0.84 for s = 5/2. Finally, we demonstrate the usefulness of our present results for E(N,S,s) by examining the Fe12 ring-type magnetic molecule, leading to a new, more accurate estimate of the exchange constant for this system than has been obtained heretofore.Comment: Submitted to Physical Review B, 10 pages, 10 figure

Low temperature magnetic properties and spin dynamics in single crystals of Cr8Zn antiferromagnetic molecular rings

Under the terms of the CC BY license.-- et al.A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring CrZn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μH = 2.15 T is found to be an almost true LC while the second LC at μH = 6.95 T has an anti-crossing gap of Δ = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μH = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in the nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ∼ 10 rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.This work was financially supported by the Italian FIRB Project No. RBFR12RPD1 of the Italian MIUR “New Challenges in Molecular Nanomagnetism: From Spin Dynamics to Quantum-Information Processing.”Peer Reviewe

Improving the effectiveness and efficiency of outpatient services: A scoping review of interventions at the primary-secondary care interface

This is the final published version. Available from SAGE Publications via the DOI in this record.Objectives: Variation in patterns of referral from primary care can lead to inappropriate overuse or underuse of specialist resources. Our aim was to review the literature on strategies involving primary care that are designed to improve the effectiveness and efficiency of outpatient services. Methods: A scoping review to update a review published in 2006. We conducted a systematic literature search and qualitative evidence synthesis of studies across five intervention domains: transfer of services from hospital to primary care; relocation of hospital services to primary care; joint working between primary care practitioners and specialists; interventions to change the referral behaviour of primary care practitioners and interventions to change patient behaviour. Results: The 183 studies published since 2005, taken with the findings of the previous review, suggest that transfer of services from secondary to primary care and strategies aimed at changing referral behaviour of primary care clinicians can be effective in reducing outpatient referrals and in increasing the appropriateness of referrals. Availability of specialist advice to primary care practitioners by email or phone and use of store-and-forward telemedicine also show potential for reducing outpatient referrals and hence reducing costs. There was little evidence of a beneficial effect of relocation of specialists to primary care, or joint primary/secondary care management of patients on outpatient referrals. Across all intervention categories there was little evidence available on cost-effectiveness. Conclusions: There are a number of promising interventions which may improve the effectiveness and efficiency of outpatient services, including making it easier for primary care clinicians and specialists to discuss patients by email or phone. There remain substantial gaps in the evidence, particularly on cost-effectiveness, and new interventions should continue to be evaluated as they are implemented more widely. A move for specialists to work in the community is unlikely to be cost-effective without enhancing primary care clinicians’skills through education or joint consultations with complex patients.National Institute for Health Research (NIHR

g-engineering in hybrid rotaxanes to create AB and AB2 electron spin systems: EPR spectroscopic studies of weak interactions between dissimilar electron spin qubits

Hybrid [2]rotaxanes and pseudorotaxanes are reported where the magnetic interaction between dissimilar spins is controlled to create AB and AB2 electron spin systems,allowing independent control of weakly interacting S =1=2 centers

Spin dynamics of heterometallic Cr7M wheels (M = Mn, Zn, Ni) probed by inelastic neutron scattering

Inelastic neutron scattering has been applied to the study of the spin dynamics of Cr-based antiferromagnetic octanuclear rings where a finite total spin of the ground state is obtained by substituting one Cr(III) ion (s = 3/2) with Zn (s = 0), Mn (s = 5/2) or Ni (s = 1) di-cations. Energy and intensity measurements for several intra-multiplet and inter-multiplet magnetic excitations allow us to determine the spin wavefunctions of the investigated clusters. Effects due to the mixing of different spin multiplets have been considered. Such effects proved to be important to correctly reproduce the energy and intensity of magnetic excitations in the neutron spectra. On the contrary to what is observed for the parent homonuclear Cr8 ring, the symmetry of the first excited spin states is such that anticrossing conditions with the ground state can be realized in the presence of an external magnetic field. Heterometallic Cr7M wheels are therefore good candidates for macroscopic observations of quantum effects.Comment: 9 pages, 11 figures, submitted to Phys. Rev. B, corrected typos and added references, one sentence change

Bounding and approximating parabolas for the spectrum of Heisenberg spin systems

We prove that for a wide class of quantum spin systems with isotropic Heisenberg coupling the energy eigenvalues which belong to a total spin quantum number S have upper and lower bounds depending at most quadratically on S. The only assumption adopted is that the mean coupling strength of any spin w.r.t. its neighbours is constant for all N spins. The coefficients of the bounding parabolas are given in terms of special eigenvalues of the N times N coupling matrix which are usually easily evaluated. In addition we show that the bounding parabolas, if properly shifted, provide very good approximations of the true boundaries of the spectrum. We present numerical examples of frustrated rings, a cube, and an icosahedron.Comment: 8 pages, 3 figures. Submitted to Europhysics Letter

Outpatient services and primary care: scoping review, substudies and international comparisons

This is the final version of the report. Available from the publisher via the DOI in this record.AIM: This study updates a previous scoping review published by the National Institute for Health Research (NIHR) in 2006 (Roland M, McDonald R, Sibbald B. Outpatient Services and Primary Care: A Scoping Review of Research Into Strategies For Improving Outpatient Effectiveness and Efficiency. Southampton: NIHR Trials and Studies Coordinating Centre; 2006) and focuses on strategies to improve the effectiveness and efficiency of outpatient services. FINDINGS FROM THE SCOPING REVIEW: Evidence from the scoping review suggests that, with appropriate safeguards, training and support, substantial parts of care given in outpatient clinics can be transferred to primary care. This includes additional evidence since our 2006 review which supports general practitioner (GP) follow-up as an alternative to outpatient follow-up appointments, primary medical care of chronic conditions and minor surgery in primary care. Relocating specialists to primary care settings is popular with patients, and increased joint working between specialists and GPs, as suggested in the NHS Five Year Forward View, can be of substantial educational value. However, for these approaches there is very limited information on cost-effectiveness; we do not know whether they increase or reduce overall demand and whether the new models cost more or less than traditional approaches. One promising development is the increasing use of e-mail between GPs and specialists, with some studies suggesting that better communication (including the transmission of results and images) could substantially reduce the need for some referrals. FINDINGS FROM THE SUBSTUDIES: Because of the limited literature on some areas, we conducted a number of substudies in England. The first was of referral management centres, which have been established to triage and, potentially, divert referrals away from hospitals. These centres encounter practical and administrative challenges and have difficulty getting buy-in from local clinicians. Their effectiveness is uncertain, as is the effect of schemes which provide systematic review of referrals within GP practices. However, the latter appear to have more positive educational value, as shown in our second substudy. We also studied consultants who held contracts with community-based organisations rather than with hospital trusts. Although these posts offer opportunities in terms of breaking down artificial and unhelpful primary–secondary care barriers, they may be constrained by their idiosyncratic nature, a lack of clarity around roles, challenges to professional identity and a lack of opportunities for professional development. Finally, we examined the work done by other countries to reform activity at the primary–secondary care interface. Common approaches included the use of financial mechanisms and incentives, the transfer of work to primary care, the relocation of specialists and the use of guidelines and protocols. With the possible exception of financial incentives, the lack of robust evidence on the effect of these approaches and the contexts in which they were introduced limits the lessons that can be drawn for the English NHS. CONCLUSIONS: For many conditions, high-quality care in the community can be provided and is popular with patients. There is little conclusive evidence on the cost-effectiveness of the provision of more care in the community. In developing new models of care for the NHS, it should not be assumed that community-based care will be cheaper than conventional hospital-based care. Possible reasons care in the community may be more expensive include supply-induced demand and addressing unmet need through new forms of care and through loss of efficiency gained from concentrating services in hospitals. Evidence from this study suggests that further shifts of care into the community can be justified only if (a) high value is given to patient convenience in relation to NHS costs or (b) community care can be provided in a way that reduces overall health-care costs. However, reconfigurations of services are often introduced without adequate evaluation and it is important that new NHS initiatives should collect data to show whether or not they have added value, and improved quality and patient and staff experience.The NIHR Health Services and Delivery Research programme

Molecular engineering of antiferromagnetic rings for quantum computation

The substitution of one metal ion in a Cr-based molecular ring with dominant antiferromagnetic couplings allows to engineer its level structure and ground-state degeneracy. Here we characterize a Cr7Ni molecular ring by means of low-temperature specific-heat and torque-magnetometry measurements, thus determining the microscopic parameters of the corresponding spin Hamiltonian. The energy spectrum and the suppression of the leakage-inducing S-mixing render the Cr7Ni molecule a suitable candidate for the qubit implementation, as further substantiated by our quantum-gate simulations.Comment: To appear in Physical Review Letter