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.

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 beß=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.

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.

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.

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.

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.

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.

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.

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.

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) µB at 1.5 K. The magnetic Bragg intensity grows very slowly below 1 K, reaching ~2.4 µB 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.

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].

A quantitative stability analysis of human monoclonal antibody production by heteromyeloma hybridomas, using an immunofluorescent technique.

We describe a quantitative method of analysis for assessing stability of human monoclonal antibody production by hybridomas. Clones derived from fusion between the SHM-D33 heteromyeloma line and EBV-stimulated human lymphocytes were studied for antibody presence using a fluorescent labelling technique. Frequencies of antibody-negative variants in clonal populations were measured, and measurements on parallel clonal populations were subjected to Luria-Delbrück fluctuation analysis to compute rates of generations of antibody-negative cells. Independent hybridoma clones exhibited a range of stabilities and the corresponding rates varied between 5 X 10(-4) and 6 X 10(-2) cell-1 generation-1. Rates of generation of antibody-negative variants for the more stable heteromyeloma hybridomas compared well with those of 2 established mouse hybridoma lines tested (less than 10(-3) cell-1 generation-1). There was a positive correlation between frequency of antibody-negative variants measured in clonal populations grown to large numbers of cells (greater than 10(7) per culture) and their rate of loss of antibody production. Large variations in frequency of antibody-negative variants were observed in parallel clonal populations, suggesting that loss of ability to produce antibody is due to random, mutation-like events including chromosome loss (Luria and Delbrück, 1943). High frequencies of antibody-negative variants may indicate imminent loss of antibody-producing capacity by a clone growing in suspension culture.

Maternal exposure to prescription and non-prescription pharmaceuticals or drugs of abuse and risk of craniosynostosis.

BACKGROUND: The pre- and peri-natal drug exposures reported by women participating in a case-control study of children in Colorado were examined for association with infant craniosynostosis. METHODS: Mothers of case and control children underwent a standardized telephone interview and obstetric and newborn medical record review. The interview included questions on the use of prescription and non-prescription drugs, nutritional supplements, recreational and drugs of abuse. The mother's obstetric record was abstracted for information about pharmacologic agents taken before and during the antepartum period. RESULTS: There were no statistically significant risk ratios associating craniosynostosis with prenatal exposure to hydantoin, valproic acid, or cocaine. Mothers of four case children and one control child reported specific exposure to retinoic acid. There were no statistically significant increases in the odds ratio (OR) for any suture type among children exposed to hypoxigenic agents, sympathomimetic or parasympatholytic agents, or metal-containing agents. The OR was 1.87 (lower bound of the two-sided 95% test-based confidence interval (CI): 1.08) among children with sagittal/lambdoid suture synostosis who were exposed to nitrosatable drugs chlorpheniramine, chlordiazepoxide, and nitrofurantoin compared to controls. CONCLUSIONS: Certain nitrosatable drugs may be associated with increased risk of infant sagittal/lambdoid craniosynostosis. A possible mechanism related to ischaemia/reperfusion injury is suggested.

Solid-phase, magnetic particle radioimmunoassay.

A solid-phase radioimmunoassay system has been developed based on the use of antibodies covalently linked to polymer-coated iron oxide (EnzacrylR). An electro-magnet is employed both to mix the particles during incubation (by switching the field on and off) and to separate the antibody-bound and free fractions. This obviates the need for vertical rotation and for the time-consuming, multiple centrifugations required with conventional solid phase procedures. The system is universally applicable and methods have been established for the assay of thyroxine, human placental lactogen and digoxin. The thyroxine assay was employed as a model and it was shown that the results obtained for serum samples correlated closely with those using a routine liquid-phase radioimmunoassay. The applicability of employing a second antibody linked to the iron oxide particles was also studied.

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.

Medical records and privacy: empirical effects of legislation.

OBJECTIVE: To determine the effects of state legislation requiring patient informed consent prior to medical record abstraction by external researchers for a specific study. DATA SOURCES/STUDY SETTING: Informed consent responses obtained from November 1997 through April 1998 from members of a Minnesota-based IPA model health plan. STUDY DESIGN: Descriptive case study of consent to gain access to medical records for a pharmaco-epidemiologic study of seizures associated with use of a pain medication that was conducted as part of the FDA's post-marketing safety surveillance program to evaluate adverse events associated with approved drugs. DATA COLLECTION: The informed consent process approved by an institutional review board consisted of three phases: (1) a letter from the health plan's medical director requesting participation, (2) a second mailing to nonrespondents, and (3) a follow-up telephone call to nonrespondents. PRINCIPAL FINDINGS: Of 140 Minnesota health plan members asked to participate in the medical records study, 52 percent (73) responded and 19 percent (26) returned a signed consent form authorizing access to their records for the study. For 132 study subjects enrolled in five other health plans in states where study-specific consent was not required, health care providers granted access to patient medical records for 93 percent (123) of the members. CONCLUSION: Legislation requiring patient informed consent to gain access to medical records for a specific research study was associated with low participation and increased time to complete that observational study. Efforts to protect patient privacy may come into conflict with the ability to produce timely and valid research to safeguard and improve public health.

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.

Therapeutic interchange of conjugated and esterified estrogens in a managed care organization.

A program designed to curb increases in drug costs in an HMO by substituting esterified for conjugated estrogens was developed and studied. Patients were voluntarily switched from conjugated to esterified estrogens at an HMO in Washington State. Women were informed about the conversion through newsletters and during clinic and pharmacy visits and received physician and pharmacist counseling. Cost savings were estimated, and patient acceptance was evaluated by interviewing women in four groups, including women who were switched from conjugated to esterified estrogens and then switched back (C-E-C group), women who were not switched (C-C group), and women who were switched to esterified estrogens and not switched back (C-E group). During the first six months, 14,601 (89.2%) of 16,364 women taking conjugated estrogens were switched to esterified estrogens; of these, 13,654 (93.5%) continued taking esterified estrogens for at least six months. The HMO avoided $653,119 of an expected $750,000 cost increase for oral estrogen therapy during the first year of the program. A total of 754 women were interviewed; 65.8% in the C-E-C group and 78.4% in the C-E group reported being satisfied with the information they received. The conversion experience was rated as positive by 28.3% of women in the C-E-C group and 41.5% of women in the C-E group, negative by 25.1%, and 8.9%, and neutral by 46.6% and 49.6%. An HMO avoided a large increase in drug costs by substituting esterified for conjugated estrogens; only 6.5% of patients were switched back to conjugated estrogens at their physicians' or their own request; most patients thought the conversion was a neutral or positive experience.

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.

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.