Emergence of the isotropic Kitaev honeycomb latticeα-RuCl3and its magnetic properties

We present a comprehensive investigation of the crystal and magnetic structures of the van der Waals antiferromagnetα-RuCl3using single crystal x-ray and neutron diffraction. The crystal structure at room temperature is a monoclinic (C2/m). However, with decreasing temperature, a remarkable first-order structural phase transition is observed, leading to the emergence of a rhombohedral (R3-) structure characterized by three-fold rotational symmetry forming an isotropic honeycomb lattice. On further cooling, a zigzag-type antiferromagnetic order develops belowTN=6∼6.6K. The critical exponent of the magnetic order parameter was determined to beβ=0.11(1), which is close to the two-dimensional Ising model. Additionally, the angular dependence of the magnetic critical field of the zigzag antiferromagnetic order for the polarized ferromagnetic phase reveals a six-fold rotational symmetry within theab-plane. These findingsreflect the symmetry associated with the Ising-like bond-dependent Kitaev spin interactions and underscore the universality of the Kitaev interaction-dominated antiferromagnetic system.

TCR+/BCR+ dual-expressing cells and their associated public BCR clonotype are not enriched in type 1 diabetes

Ahmed and colleagues recently described a novel hybrid lymphocyte expressing both a B and T cell receptor, termed double expresser (DE) cells. DE cells in blood of type 1 diabetes (T1D) subjects were present at increased numbers and enriched for a public B cell clonotype. Here, we attempted to reproduce these findings. While we could identify DE cells by flow cytometry, we found no association between DE cell frequency and T1D status. We were unable to identify the reported public B cell clone, or any similar clone, in bulk B cells or sorted DE cells from T1D subjects or controls. We also did not observe increased usage of the public clone VH or DH genes in B cells or in sorted DE cells. Taken together, our findings suggest that DE cells and their alleged public clonotype are not enriched in T1D. This Matters Arising paper is in response to Ahmed et al. (2019), published in Cell. See also the response by Ahmed et al. (2021), published in this issue.

Spin-Glass Ground State in a Triangular-Lattice Compound YbZnGaO_{4}

We report on comprehensive results identifying the ground state of a triangular-lattice structured YbZnGaO_{4} as a spin glass, including no long-range magnetic order, prominent broad excitation continua, and the absence of magnetic thermal conductivity. More crucially, from the ultralow-temperature ac susceptibility measurements, we unambiguously observe frequency-dependent peaks around 0.1 K, indicating the spin-glass ground state. We suggest this conclusion holds also for its sister compound YbMgGaO_{4}, which is confirmed by the observation of spin freezing at low temperatures. We consider disorder and frustration to be the main driving force for the spin-glass phase.

Evidence for the confinement of magnetic monopoles in quantum spin ice

Magnetic monopoles are hypothesised elementary particles connected by Dirac strings that behave like infinitely thin solenoids (Dirac 1931 Proc. R. Soc. A 133 60). Despite decades of searching, free magnetic monopoles and their Dirac strings have eluded experimental detection, although there is substantial evidence for deconfined magnetic monopole quasiparticles in spin ice materials (Castelnovo et al 2008 Nature 326 411). Here we report the detection of a hierarchy of unequally-spaced magnetic excitations via high resolution inelastic neutron spectroscopic measurements on the quantum spin ice candidate [Formula: see text] [Formula: see text] [Formula: see text]. These excitations are well-described by a simple model of monopole pairs bound by a linear potential (Coldea et al Science 327 177) with an effective tension of 0.642(8) K [Formula: see text] at 1.65 K. The success of the linear potential model suggests that these low energy magnetic excitations are direct spectroscopic evidence for the confinement of magnetic monopole quasiparticles in the quantum spin ice candidate [Formula: see text] [Formula: see text] [Formula: see text].

Magnetic correlations in the intermetallic antiferromagnet Nd3Co4Sn13

Specific heat, magnetic susceptibility, and neutron scattering have been used to investigate the nature of the spin system in the antiferromagnet Nd₃Co₄Sn₁₃. At room temperature Nd₃Co₄Sn₁₃ has a cubic, Pm-3n structure similar to Yb₃Rh₄Sn₁₃. Antiferromagnetic interactions between, Nd³⁺ ions dominate the magnetic character of this sample and at 2.4 K the Nd spins enter a long range order state with a magnetic propagation vector q  =  (0 0 0) with an ordered moment of 1.78(2) µ_B at 1.5 K. The magnetic Bragg intensity grows very slowly below 1 K, reaching ~2.4 µ_B at 350 mK. The average magnetic Nd³⁺ configuration corresponds to the 3D irreducible representation Γ₇. This magnetic structure can be viewed as three sublattices of antiferromagnetic spin chains coupled with each other in the 120°-configuration. A well-defined magnetic excitation was measured around the 1 1 1 zone centre and the resulting dispersion curve is appropriate for an antiferromagnet with a gap of 0.20(1) meV.

A detailed study of the magnetic phase transition in CuCrO2

The phase transition in CuCrO2 to an ordered magnetic state is studied with bulk measurements and elastic and inelastic neutron scattering techniques. The reported onset of spontaneous electric polarization at T = 23.5 K coincides with the appearance, on cooling, of elastic magnetic scattering. At higher temperatures long range magnetic correlations gradually develop but they are dynamic. The ground state is characterized by three-dimensional long range magnetic ordering but along the c direction the correlation length remains limited to ∼200 Å.

Successive phase transitions and extended spin-excitation continuum in the S=1/2 triangular-lattice antiferromagnet Ba3CoSb2O9

Using magnetic, thermal, and neutron measurements on single-crystal samples, we show that Ba3CoSb2O9 is a spin-1/2 triangular-lattice antiferromagnet with the c axis as the magnetic easy axis and two magnetic phase transitions bracketing an intermediate up-up-down phase in magnetic field applied along the c axis. A pronounced extensive neutron-scattering continuum above spin-wave excitations, observed below T(N), implies that the system is in close proximity to one of two spin-liquid states that have been predicted for a 2D triangular lattice.

First order metamagnetic transition in Ho2Ti2O7 observed by vibrating coil magnetometry at Milli-Kelvin temperatures

We report vibrating coil magnetometry of the spin-ice system Ho(2)Ti(2)O(7) down to ~0.04 K for magnetic fields up to 5 T applied parallel to the [111] axis. History-dependent behavior emerges below T(0)(*) ~ 0.6 K near zero magnetic field, in common with other spin-ice compounds. In large magnetic fields, we observe a magnetization plateau followed by a hysteretic metamagnetic transition. The temperature dependence of the coercive fields as well as the susceptibility calculated from the magnetization identify the metamagnetic transition as a line of first order transitions terminating in a critical end point at T(m)(*) 0.37 ~/= K, B(m) ~/= 1.5 T. The metamagnetic transition in Ho(2)Ti(2)O(7) is strongly reminiscent of that observed in Dy(2)Ti(2)O(7), suggestive of a general feature of the spin ices.

Chemical pressure effects on pyrochlore spin ice

A comparison among the two sets of studied pyrochlore spin ices, Ho2Sn2O7, Ho2Ti2O7, and Ho2Ge2O7 with Ho3+ spins and Dy2Sn2O7, Dy2Ti2O7, and Dy2Ge2O7 with Dy3+ spins, shows that the application of chemical pressure through each set drives the system toward the antiferromagnetic phase boundary from the spin ice region, which agrees with the prediction of the "dipolar spin ice" model of den Hertog and Gingras. Among all the studied pyrochlore spin ices, Dy2Ge2O7 has the smallest ratio of Jnn/Dnn=-0.73.

Low energy spin dynamics in the spin ice Ho2Sn2O7

The magnetic properties of Ho(2)Sn(2)O(7) have been investigated and compared to other spin ice compounds. Although the lattice has expanded by 3% relative to the better studied Ho(2)Ti(2)O(7) spin ice, no significant changes were observed in the high temperature properties, T is more or approximately equal to 20 K. As the temperature is lowered and correlations develop, Ho(2)Sn(2)O(7) enters its quantum phase at a slightly higher temperature than Ho(2)Ti(2)O(7) and is more antiferromagnetic in character. Below 80 K a weak inelastic mode associated with the holmium nuclear spin system has been measured. The hyperfine field at the holmium nucleus was found to be ≈700 T.

Absence of long-range magnetic ordering in the pyrochlore compound Er2Sn2O7

The low temperature behaviour of powder Er2Sn2O7 samples has been studied by magnetic susceptibility, heat capacity, and neutron scattering experiments. We report here the absence of magnetic ordering down to 100 mK. Anomalies in the heat capacity can be accounted for through an analysis of the crystal field spectrum observed by inelastic neutron scattering spectroscopy. These new measurements on Er2Sn2O7 suggest a new lower bound for the frustration index of f = |Θ(CW)|/T(N) = 14/0.1 = 140, placing this compound into a highly frustrated regime.

High pressure route to generate magnetic monopole dimers in spin ice

The gas of magnetic monopoles in spin ice is governed by one key parameter: the monopole chemical potential. A significant variation of this parameter could access hitherto undiscovered magnetic phenomena arising from monopole correlations, as observed in the analogous electrical Coulomb gas, like monopole dimerization, critical phase separation, or charge ordering. However, all known spin ices have values of chemical potential imposed by their structure and chemistry that place them deeply within the weakly correlated regime, where none of these interesting phenomena occur. Here we use high-pressure synthesis to create a new monopole host, Dy(2)Ge(2)O(7), with a radically altered chemical potential that stabilizes a large fraction of monopole dimers. The system is found to be ideally described by the classic Debye-Huckel-Bjerrum theory of charge correlations. We thus show how to tune the monopole chemical potential in spin ice and how to access the diverse collective properties of magnetic monopoles.

Short range ordering in the modified honeycomb lattice compound SrHo(2)O(4)

The low temperature behaviour of single crystalline SrHo(2)O(4) has been characterized by dc magnetic susceptibility, heat capacity, and neutron scattering experiments. Our results show that despite the lack of magnetic long-ranged ordering in the presence of strong antiferromagnetic correlations, SrHo(2)O(4) does not order down to 1.8 K. Elastic neutron scattering experiments show prominent magnetic diffuse scattering correlated with a broad feature in the dc susceptibility at T = 4 K, indicative of magnetic short-ranged ordering of the Ho(3) spins. Inelastic neutron scattering shows the presence of five crystal field levels up to 80 K in energy, in agreement with the integration of the magnetic specific heat component yielding Rln5 entropy release. The magnetic short-ranged ordering is fitted to a nearest neighbour interaction model with good agreement.

Slow and static spin correlations in Dy(2 + x)Ti(2 - x)O(7 - δ)

The static and dynamic spin correlations in the spin ices Dy(2.3)Ti(1.7)O(6.85) and Dy(2)Ti(2)O(7) have been studied in polarized neutron diffraction and neutron spin echo experiments. The measurements reveal that, below 100 mK, the magnetic scattering broadens and shifts to higher |Q| upon stuffing the pyrochlore lattice with additional Dy(3+) ions. These observations can be related, by means of reverse Monte Carlo simulation, to the modified distribution of near-neighbour distances and an overall more antiferromagnetic character of the near-neighbour couplings. The dynamic measurements show that the spin correlations are slower in the stuffed system. These results will be discussed and compared to the holmium analogues.

The magnetic phase diagram of Gd(2)Sn(2)O(7)

Measurements of the magnetic susceptibility of the frustrated pyrochlore magnet Gd(2)Sn(2)O(7) have been performed at temperatures below T = 5 K and in magnetic fields up to H = 12 T. The phase boundaries determined from these measurements are mapped out in an H-T phase diagram. In this gadolinium compound, where the crystal-field splitting is small and the exchange and dipolar energy are comparable, the Zeeman energy overcomes these competing energies, resulting in at least four magnetic phase transitions below 1 K. These data are compared against those for Gd(2)Ti(2)O(7) and will, we hope, stimulate further studies.

Spin liquid state in the S = 1/2 triangular lattice Ba3CuSb2O9

The synthesis and characterization of Ba3CuSb2O9, which has a layered array of Cu2+ spins in a triangular lattice, are reported. The magnetic susceptibility and neutron scattering experiments of this material show no magnetic ordering down to 0.2 K with a θ(CW) = -55  K. The magnetic specific heat reveals a T-linear dependence with a γ = 43.4  mJ  K(-2)  mol(-1) below 1.4 K. These observations suggest that Ba3CuSb2O9 is a new quantum spin liquid candidate with a S = 1/2 triangular lattice.

Magnetic order in the double pyrochlore Tb₂Ru₂O₇

Polycrystalline Tb(2)Ru(2)O(7) has been studied using dc susceptibility, specific heat and neutron scattering techniques. The high temperature paramagnetic state is dominated by the single ion character of Tb(3 + ) and very similar to that of the well-studied spin liquid Tb(2)Ti(2)O(7). However, both the Ru(4 + ) and Tb(3 + ) sublattices order, at about 110 K and 3.5 K, respectively. Although the Tb sublattice does not fully order until 3.5 K, it is polarized in the presence of the internal field generated by the Ru(4 + ) sublattice and possesses a significant moment at 7 K. Magnetic entropy measurements suggest that four levels exist in the first 30 K and inelastic neutron scattering investigations revealed two more levels at 10 and 14 meV. As the magnetic sublattices order, the excitations are perturbed from that measured in the paramagnetic state. These data are compared to data for other terbium based and double pyrochlores.

Neutron scattering investigations of the partially ordered pyrochlore Tb(2)Sn(2)O(7)

Neutron scattering measurements have been performed on polycrystalline Tb(2)Sn(2)O(7) at temperatures above and below that of the phase transition, T(N) = 0.87 K, to investigate further the spin dynamics in the magnetically ordered state. In particular, new neutron spin echo results are presented showing a dependence on Q in the dynamics. We show evidence of the coexistence of static ferromagnetism and dynamically fluctuating spins down to 30 mK and we make a comparison of this partially ordered system to the spin liquid Tb(2)Ti(2)O(7).

Two-dimensional kagome correlations and field induced order in the ferromagnetic XY pyrochlore Yb2Ti2O7

Neutron scattering measurements show the ferromagnetic XY pyrochlore Yb2Ti2O7 to display strong quasi-two-dimensional (2D) spin correlations at low temperature, which give way to long range order (LRO) under the application of modest magnetic fields. Rods of scattering along 111 directions due to these 2D spin correlations imply a magnetic decomposition of the cubic pyrochlore system into decoupled kagome planes. A magnetic field of approximately 0.5 T applied along the [110] direction induces a transition to a 3D LRO state characterized by long-lived, dispersive spin waves. Our measurements map out a complex low temperature-field phase diagram for this exotic pyrochlore magnet.

Magnetic order and crystal field excitations in Er(2)Ru(2)O(7): a neutron scattering study

The magnetic pyrochlore Er(2)Ru(2)O(7) has been studied with neutron scattering and susceptibility measurements down to a base temperature of 270 mK. For the low temperature phase in which the Er sublattice orders, new magnetic Bragg peaks are reported which can be indexed with integer (hkl) for a face centered cubic cell. Inelastic measurements reveal a wealth of crystal field levels of the Er ion and a copious amount of magnetic scattering below 15 meV. The three lowest groups of crystal field levels are at 6.7, 9.1 and 18.5 meV.

Chemical pressure induced spin freezing phase transition in kagome pr langasites

The 2D kagome system Pr3Ga5SiO14 has been previously identified as a spin-liquid candidate in zero field, displaying no magnetic long-ranged order down to at least 35 mK. Perturbations upon such systems, either under applied fields or applied pressure, should induce a spin freezing phase transition, but there are very few experimental realizations of this phenomena other than the well-studied 3D pyrochlore Tb2Ti2O7. In this Letter, we report the observation of a spin freezing phase transition in Pr3Ga5SiO14 through the application of chemical pressure--that is, through a systematic substitution on the Si site with larger ions and an elongation of the nearest-neighbor Pr-Pr distance in the kagome lattice. This results in a suppression of the T2 component of the heat capacity, and the reduction of the exchange constant eventually leads to dipolar-driven spin freezing.

Direct observation of a nuclear spin excitation in Ho2Ti2O7

A single nondispersive excitation is observed by means of neutron backscattering, at E_{0}=26.3 microeV in the spin ice Ho2Ti2O7 but not in the isotopically enriched 162Dy2Ti2O7 analogue. The intensity of this excitation is rather small, less, similar0.2% of the elastic intensity. It is clearly observed below 80 K but resolution limited only below approximately 65 K. The application of a magnetic field up to micro_{0}H=4.5 T, at 1.6 K, has no measurable effect on the energy or intensity. This nuclear excitation is believed to perturb the electronic, Ising spin system resulting in the persistent spin dynamics observed in spin ice compounds.

Static magnetic order in Tb2Sn2O7 revealed by muon spin relaxation with exterior muon implantation

Tb2Sn2O7 has been proposed as an ordered spin ice, but the precise nature of the low temperature magnetic state remains uncertain. Recent independent muon spin relaxation (microSR) investigations suggest the possibility of exotic ground states with static order precluded on time scales longer than 10(-6) s. Here the more conventional hypothesis of canted ferromagnetism is tested by means of microSR with the muons stopped outside the sample, as well as ultralow field bulk magnetization measurements. The field cooled state shows conventional static order, while the zero field cooled state may be interpreted in terms of conventional closed domains. These results rule out purely dynamical ground states and illustrate the value of exterior muon implantation as a complement to the conventional technique.

Dynamic spin ice: Pr2Sn2O7

In this Letter, we report a new spin ice--Pr2Sn2O7--which appears to have enhanced residual entropy due to the dynamic nature of the spins. Neutron scattering experiments show that at 200 mK, there is a significant amount of magnetic diffuse scattering which can be fit to the dipolar spin-ice model. However, these short-ranged ordered spins have a quasielastic response that is atypical of the canonical spin ices, and suggests that the ground state is dynamic (i.e., composed of locally ordered two-in-two-out spin configurations that can tunnel between energetically equivalent orientations). We report this as an example of a dynamic spin ice down to 200 mK.

Spin waves and quantum criticality in the frustrated XY pyrochlore antiferromagnet Er2Ti2O7

We report detailed measurements of the low temperature magnetic phase diagram of Er2Ti2O7. Heat capacity and time-of-flight neutron scattering studies of single crystals reveal unconventional low-energy states. Er3+ magnetic ions reside on a pyrochlore lattice in Er2Ti2O7, where local XY anisotropy and antiferromagnetic interactions give rise to a unique frustrated system. In zero field, the ground state exhibits coexisting short and long-range order, accompanied by soft collective spin excitations previously believed to be absent. The application of finite magnetic fields tunes the ground state continuously through a landscape of noncollinear phases, divided by a zero temperature phase transition at micro{0}H{c} approximately 1.5 T. The characteristic energy scale for spin fluctuations is seen to vanish at the critical point, as expected for a second order quantum phase transition driven by quantum fluctuations.

Frustrated spin correlations in diluted spin ice Ho(2-x)La(x)Ti(2)O(7)

We have studied the evolution of the structural properties as well as the static and dynamic spin correlations of spin ice Ho(2)Ti(2)O(7), where Ho was partially replaced by non-magnetic La. The crystal structure of diluted samples Ho(2-x)La(x)Ti(2)O(7) was characterized by x-ray and neutron diffraction and by Ho L(III)-edge and Ti K-edge extended x-ray absorption fine structure (EXAFS) measurements. It is found that the pyrochlore structure remains intact until about x = 0.3, but a systematic increase in local disorder with increasing La concentration is observed in the EXAFS data, especially from the Ti K edge. Quasi-elastic neutron scattering and ac susceptibility measurements show that, in x≤0.4 samples at temperatures above macroscopic freezing, the spin-spin correlations are short ranged and dynamic in nature. The main difference with pure spin ice in the dynamics is the appearance of a second, faster, relaxation process.

Partial field-induced magnetic order in the spin-liquid kagomé Nd3Ga5SiO14

The distorted kagomé system Nd3Ga5SiO14 has been investigated with neutron scattering down to 0.046 K with no evidence of magnetic long range order of the Nd3+ moments in a zero field. Substantial diffuse scattering is observed which is in agreement with nearest-neighbor correlations between the fluctuating spins. Upon the application of a field in the c direction, the diffuse scattering is reduced in intensity while the magnetic Bragg peaks grow in intensity to saturate by 1 T to 1/2 of the expected magnetization. These measurements suggest that a unique spin-liquid state develops in Nd3Ga5SiO14 with a frustration index of f approximately |theta|/T_{C}> or =1300.

Field-induced order and spin waves in the pyrochlore antiferromagnet Tb2Ti207

High resolution time-of-flight neutron scattering measurements on Tb(2)Ti(2)0(7) reveal a rich low temperature phase diagram in the presence of a magnetic field applied along [110]. In zero field at T = 0.4 K, Tb(2)Ti(2)0(7) is a highly correlated cooperative paramagnet with disordered spins residing on a pyrochlore lattice of corner-sharing tetrahedra. Application of a small field condenses much of the magnetic diffuse scattering, characteristic of the disordered spins, into a new Bragg peak characteristic of a polarized paramagnet. At higher fields, a magnetically ordered phase is induced, which supports spin wave excitations indicative of continuous, rather than Ising-like, spin degrees of freedom.

Novel coexistence of superconductivity with two distinct magnetic orders

The heavy fermion system exhibits properties that range from an incommensurate antiferromagnet for small to an exotic superconductor on the Ir-rich end of the phase diagram. At intermediate where antiferromagnetism coexists with superconductivity, two types of magnetic order are observed: the incommensurate one of and a new, commensurate antiferromagnetism that orders separately. The coexistence of -electron superconductivity with two distinct -electron magnetic orders is unique among unconventional superconductors, adding a new variety to the usual coexistence found in magnetic superconductors.

Magnetic ordering in the spin-ice candidate Ho2Ru2O7

Neutron scattering measurements on the spin-ice candidate material Ho2Ru2O7 have revealed two magnetic transitions at T approximately 95 and approximately 1.4 K to long-range ordered states involving the Ru and Ho sublattices, respectively. Between these transitions, the Ho3+ moments form short-ranged ordered spin clusters. The internal field provided by the ordered S=1 Ru4+ moments disrupts the fragile spin-ice state and drives the Ho3+ moments to order. We have directly measured a slight shift in the Ho3+ crystal field levels at 95 K from the Ru ordering.

Cohort maintenance and comparability in a pharmacoepidemiologic study using a commercial consumer panel to recruit comparators

The Upjohn Consumer Health Survey (UCHS) was a prospective, observational study of users of ROGAINE (REGAINE in international markets) Topical Solution 2% (N=11,122) and a Comparator cohort (N=11,173) which was selected and group matched by stratified random sampling from among members of a commercial consumer panel. Study endpoints were confirmed cause-specific deaths and hospitalizations within 12 months of study entry. Data collection was accomplished by participant interviews and confirmation of participant-reported medical events. At least 94% of both cohorts completed 12 months of follow-up, with the completion rate highest in the Comparator cohort (96.8%). Although successful matching was achieved on the demographic variables used to select the Comparators, members of the two cohorts differed significantly in the presence of baseline chronic medical conditions and other risk factors for study endpoints. A commercial consumer panel is valuable for rapid selection of demographically-matched comparators for targeted cohorts which continue in the study through long-term follow-up. Multi-stage sampling may need to be employed when more specific characteristics must be identified.

Dynamic properties of a diluted pyrochlore cooperative paramagnet (Tb(p)Y(1-p))2Ti2O7

Investigations of the spin dynamics of the geometrically frustrated pyrochlore (Tb(p)Y(1-p))2Ti2O7, using muon spin relaxation and neutron spin echo, as a function of magnetic coverage p, have been carried out. Our major finding is that paramagnetic fluctuations prevail as T-->0 for all values of p, and that they are sensitive to dilution, indicating a cooperative spin motion. However, the percolation threshold pc is not a critical point for the fluctuations. We also find that the low temperature spectral density has a 1/f behavior, and that dilution slows down the spin fluctuations.

Pressure-induced crystallization of a spin liquid

Liquids are expected to crystallize at low temperature. The only exception is helium, which can remain liquid at 0 K, owing to quantum fluctuations. Similarly, the atomic magnetic moments (spins) in a magnet are expected to order at a temperature scale set by the Curie-Weiss temperature theta(CW) (ref. 3). Geometrically frustrated magnets represent an exception. In these systems, the pairwise spin interactions cannot be simultaneously minimized because of the lattice symmetry. This can stabilize a liquid-like state of short-range-ordered fluctuating moments well below theta(CW) (refs 5-7). Here we use neutron scattering to observe the spin liquid state in a geometrically frustrated system, Tb(2)Ti(2)O(7), under conditions of high pressure (approximately 9 GPa) and low temperature (approximately 1 K). This compound is a three-dimensional magnet with theta(CW) = -19 K, where the negative value indicates antiferromagnetic interactions. At ambient pressure Tb(2)Ti(2)O(7) remains in a spin liquid state down to at least 70 mK (ref. 8). But we find that, under high pressure, the spins start to order or 'crystallize' below 2.1 K, with antiferromagnetic order coexisting with liquid-like fluctuations. These results indicate that a spin liquid/solid mixture can be induced by pressure in geometrically frustrated systems.

Temperature dependence of the magnetic penetration depth in the vortex state of the pyrochlore superconductor, Cd2Re2O7

We report transverse-field and zero-field muon spin rotation and relaxation studies of the superconducting rhenium oxide pyrochlore, Cd2Re2O7. Transverse-field measurements (H=0.007 T) show line broadening below T(c), which is characteristic of a vortex state, demonstrating conclusively the type-II nature of this superconductor. The penetration depth is seen to level off below about 400 mK (T/T(c) approximately 0.4), with a rather large value of lambda(T=0) approximately 7500 A. The temperature independent behavior below approximately 400 mK is consistent with a nodeless superconducting energy gap. Zero-field measurements indicate no static magnetic fields developing below the transition temperature.

Adolescents' use of emergency contraception provided by Washington State pharmacists

STUDY OBJECTIVE

To increase knowledge about adolescents who obtained emergency contraceptive pills (ECP) directly from a pharmacist without first contacting a physician.

DESIGN

Cross-sectional self-administered survey.

SETTING

Fifteen randomly selected pharmacies providing ECP in western Washington State.

PARTICIPANTS

Adolescents 15-21 years old (n = 126) who obtained ECP directly from a pharmacist.

OUTCOME MEASURES

Responses to a 20-item questionnaire examining adolescents' reasons for seeking care from a pharmacist, need for additional medical evaluation, risk for not receiving additional medical care, and satisfaction with care provided by the pharmacist.

RESULTS

The most common reasons for using the pharmacy were convenience (44%), lack of knowledge about alternatives (38%), and privacy (31%). If the pharmacy service were not available, 58% said they would see a doctor, 22% said they would wait to see if they got pregnant, and 20% did not know. Based on self-report, 81% of adolescents needed a new method of ongoing contraception, an evaluation for sexually transmitted disease, or both. Among these adolescents, 36% had risk factors for not receiving this care. Adolescents were satisfied with the pharmacy service; 94% said they would recommend the service to a friend.

CONCLUSIONS

ECP provision by pharmacists is a useful way to increase access to emergency contraception. However, many adolescents using ECP need additional medical care. Programs designed to increase ECP access should use these opportunities to link adolescents with more comprehensive reproductive health care services.

Frustration driven lattice distortion: an NMR investigation of Y(2)Mo(2)O(7)

We have investigated the (89)Y NMR spectrum and spin lattice relaxation, T(1), in the magnetically frustrated pyrochlore Y(2)Mo(2)O(7). We find that upon cooling the spectrum shifts, and broadens asymmetrically. A detailed examination of the low T spectrum reveals that it is constructed from multiple peaks, each shifted by a different amount. We argue that this spectrum is due to discrete lattice distortions and speculate that these distortions relieve the frustration and reduce the system's energy.

Modeling the cost and outcomes of pharmacist-prescribed emergency contraception

OBJECTIVES

This study investigated the effect on the risk and cost of unintended pregnancies of emergency contraceptive pills obtained directly from a pharmacist.

METHODS

We used a decision model to compare outcomes for private and public payers following unprotected intercourse from.

RESULTS

Obtaining emergency contraceptive pills from a pharmacy, compared with obtaining them from a physician or clinic, resulted in a $158 (95% confidence interval (CI) =$76, $269) reduction in costs for private payers and a $48 (95% CI = $16, $93) reduction for public payers.

CONCLUSIONS

Our findings suggest that under varied assumptions, obtaining emergency contraceptive pills directly from a pharmacist reduces the number of unintended pregnancies and is cost saving.

Spin correlations in Ho2Ti2O7: a dipolar spin ice system

The pyrochlore material Ho2Ti2O7 has been suggested to show "spin ice" behavior. We present neutron scattering and specific heat results that establish unambiguously that Ho2Ti2O7 exhibits spin ice correlations at low temperature. Diffuse magnetic neutron scattering is quite well described by a nearest neighbor spin ice model and very accurately described by a dipolar spin ice model. The heat capacity is well accounted for by the sum of a dipolar spin ice contribution and an expected nuclear spin contribution, known to exist in other Ho3+ salts. These results settle the question of the nature of the low temperature spin correlations in Ho2Ti2O7 for which contradictory claims have been made.

Multiparticle states in the S = 1 chain system CsNiCl3

A continuum of magnetic states has been observed by neutron scattering from the spin-1 chain compound CsNiCl3 in its disordered gapped one-dimensional phase. Results using both triple-axis and time-of-flight spectrometers show that around the antiferromagnetic point Qc = pi, the continuum lies higher in energy than the Haldane gapped excitations. At 6 K the integrated intensity of the continuum is about 12(2)% of the total spectral weight. This result is considerably larger than the 1%-3% weight predicted by the nonlinear sigma model for the three-particle continuum.

Anomalous weak magnetism in superconducting YBa2Cu3O6+x

For some time now, there has been considerable experimental and theoretical effort to understand the role of the normal-state "pseudogap" phase in underdoped high-temperature cuprate superconductors. Recent debate has centered on the question of whether the pseudogap is independent of superconductivity. We provide evidence from zero-field muon spin relaxation measurements in YBa2Cu3O6+x for the presence of small spontaneous static magnetic fields of electronic origin intimately related to the pseudogap transition. Our most significant finding is that, for optimal doping, these weak static magnetic fields appear well below the superconducting transition temperature. The two compositions measured suggest the existence of a quantum critical point somewhat above optimal doping.

Interpretation of restricted diffusion in sandstones with internal field gradients

We report on experiments to characterize internal magnetic field gradients that are caused by magnetic susceptibility differences between the solid phase and the fluids filling the pore space. Our measurements focus on low-field relaxometry of brine and oil in sandstones from various reservoirs around the world. Our results show the need to understand the dependence of internal field gradients on diffusion length, pore size- and fluid distribution in order to predict the impact of internal gradients on the interpretation of NMR experiments.

The emergency contraception collaborative prescribing experience in Washington State

OBJECTIVE

To describe how prescribers and pharmacists view the Emergency Contraceptive Pills (ECP) program, and to evaluate pharmacists' performance through the use of a consumer survey.

DESIGN

Self-administered provider satisfaction surveys were mailed 6 months after the program's inception. Consumer satisfaction surveys were distributed at the point of ECP service for return by mail.

SETTING

The program encouraged pharmacists and prescribers in western Washington to enter into collaborative prescribing agreements, increasing consumers' access to ECP.

PATIENTS OR OTHER PARTICIPANTS

Pharmacists who had attended ECP training sessions, prescribers who had authorized pharmacists to prescribe ECP, and women who had been prescribed ECP by pharmacists.

MAIN OUTCOME MEASURES

Providers' reasons for participating, attitudes toward the ECP program, and experiences with ECP as a result of the program; feedback from women receiving ECP from pharmacists.

RESULTS

309 pharmacist surveys and 55 prescriber surveys were sent, of which 159 (51%) and 27 (49%), respectively, were returned. Meeting patient needs and having a professional responsibility to participate were commonly reported reasons for ECP program involvement. Both pharmacists and prescribers (92%) reported being "satisfied" or "very satisfied" with their prescribing agreements. On the 470 consumer surveys returned out of 7,000 distributed (6.5%), pharmacists were rated highly satisfactory for their interactions with patients and the quality of information about ECP use given, but less satisfactory for information about adverse effects, recognition and follow-up of ECP failure, and regular contraceptive methods.

CONCLUSION

All participants expressed satisfaction with the ECP program. This example should support the initiation of similar programs in other states.

Tramadol and seizures: a surveillance study in a managed care population

STUDY OBJECTIVE

To investigate the occurrence of tramadol-associated seizures.

DESIGN

Retrospective cohort and case-control studies.

SETTING

UnitedHealth Group-affiliated independent practice model health plans, from different regions of the United States, contracting with large networks of physicians.

INTERVENTION

Analysis of administrative data from a large U.S. managed care population.

PATIENTS

A cohort of 9218 adult tramadol users and 37,232 concurrent nonusers.

MEASUREMENTS AND MAIN RESULTS

Fewer than 1% of users (80) had a presumed incident seizure claim after the first tramadol prescription. Risk of seizure claim was increased 2- to 6-fold among users adjusted for selected comorbidities and concomitant drugs. Risk was highest among those aged 25-54 years, those with more than four tramadol prescriptions, and those with history of alcohol abuse, stroke, or head injury. A case-control study among users was conducted to validate incident seizure outcomes from medical records. Only eight cases were confirmed, and all had cofactors associated with increased seizure risk.

CONCLUSION

In a general population, risk of seizure may be associated with long-term therapy with tramadol or the presence of cofactors, or confined to a small sensitive population subset.

Low temperature spin dynamics of the geometrically frustrated antiferromagnetic garnet Gd3Ga5O12

The low temperature spin dynamics of the geometrically frustrated antiferromagnet Gd 3Ga 5O (12) (GGG) have been investigated using muon spin relaxation. No evidence for static order is seen down to a temperature of 25 mK or a few percent of the Curie-Weiss temperature. Instead there is a linear decrease in the Gd spin fluctuation rate below 1 K which extrapolates to a small but finite value of 2 GHz at zero temperature. In terms of the spin fluctuations the system appears essentially to remain dynamic at low temperatures (T>0.02 K) and magnetic fields up to 1.8 T.

Observation of two time scales in the ferromagnetic manganite La1-xCaxMnO3, x approximately 0.3

We report new zero-field muon spin relaxation and neutron spin echo measurements in ferromagnetic (FM) (La,Ca)MnO3 which suggest at least two spatially separated regions possessing very different Mn-ion spin dynamics. One region displays diffusive relaxation, "critical slowing down" near T(C) and an increasing volume fraction below T(C), suggesting overdamped FM spin waves below T(C). The second region possesses more slowly fluctuating spins, a linewidth independent of q, and a decreasing volume fraction below T(C). The estimated length scale for the inhomogeneity is <or=30 A.

Is The Barley Endosperm a Water Reservoir for the Embryo When Germinating Seeds Are Dried?

The water content of germinating seeds fluctuates in response to water potential changes in the surrounding environment. We tested the hypothesis that the endosperm functions as a water reservoir when imbibed seeds experience drying, and we characterized water uptake and movement within barley (Hordeum vulgare cv. Triumph) caryopses (hereafter referred to as seeds). Water movement into and through germinating barley seeds during imbibition and drying was determined gravimetrically and with the fluorescent dye trisodium 8-hydroxy-1,3,6-pyrenetrisulfonate (PTS). During imbibition, embryo tissues hydrated more rapidly and reached a higher water content (g H20/g dry weight) than did the endosperm, although the endosperm eventually contained nine times as much total water. When barley seeds that had imbibed for 12 h were exposed to moderate (-4 MPa) drying, PTS solution moved from the endosperm into the shoot meristem, radicle, and scutellum, but not vice versa. Radicle emergence and elongation proceeded for up to 8 h. With harsh (-150 MPa) drying, PTS concentrated almost exclusively in the radicle. These data illustrate that the endosperm is at least a temporary water storage compartment external to the embryo itself. We speculate that water supplied by the endosperm may be important in reducing the harmful effects of drying during the critical transition period when a germinating seed changes from a desiccation-tolerant to a desiccation-intolerant organism.

Implant surface alterations from a nonmetallic ultrasonic tip

This study evaluates surface alterations produced on various implant surfaces by an ultrasonic scaler fitted with a nonmetallic tip. Commercially pure titanium and titanium alloy abutments, plasma-coated implants, and hydroxyapatite-coated implants were contacted with the nonmetallic tip for 10 seconds and then evaluated for surface changes by SEM examination. The commercially pure titanium and titanium alloy surfaces showed negligible alterations from the control, thus indicating possible clinical use as a maintenance device. More severe changes were evidenced with the plasma- and hydroxyapatite-coated surfaces.