Is U3Ni3Sn4 best described as near a quantum critical point?

Although most known non-Fermi liquid (NFL) materials are structurally or chemically disordered, the role of this disorder remains unclear. In particular, very few systems have been discovered that may be stoichiometric and well ordered. To test whether U3Ni3Sn4 belongs in this latter class, we present measurements of the x-ray absorption fine structure (XAFS) of polycrystalline and single-crystal U3Ni3Sn4 samples that are consistent with no measurable local structural disorder. We also present temperature-dependent specific heat data in applied magnetic fields as high as 8 T that show features that are inconsistent with the antiferromagnetic Griffiths' phase model, but do support the conclusion that a Fermi liquid/NFL crossover temperature increases with applied field. These results are inconsistent with theoretical explanations that require strong disorder effects, but do support the view that U3Ni3Sn4 is a stoichiometric, ordered material that exhibits NFL behavior, and is best described as being near an antiferromagnetic quantum critical point.Comment: 9 pages, 8 figures, in press with PR

Structure and Physical Properties of SrNiRu\u3csub\u3e5\u3c/sub\u3eO\u3csub\u3e11\u3c/sub\u3e Single Crystals: An \u3cem\u3eR\u3c/em\u3e-Type Ferrite Based on Ordered Kagome Nets

Single crystals of the R-type ferrite SrNiRu5O11 were grown from a chloride flux. The hexagonal crystal structure contains ruthenium located on distorted kagome nets. The low-temperature dc magnetic susceptibilities (χ⊥ and χ∥, perpendicular and parallel to the c axis, respectively) diverge as T−0.3, and do not exhibit any indication of long-range magnetic order down to 4.5 K. The electrical resistivity varies as T1.6 below 40 K, which is typical of non-Fermi liquids, and may originate from a competition between residual magnetic interactions among Ni2+ (S = 1) spins and geometrical frustration on the two-dimensional kagome lattice of Ru3+ (S = ½) spins. The transverse magnetoresistivity ρxy at constant temperature T = 5 K for current (J) -magnetic field (H) configurations, J⊥H ∥ c axis and J ∥ H⊥c axis, reveals no anomalous contribution, which is consistent with the absence of magnetic order. Fits of the specific heat data below 10 K require a dominant, but unusual electronic term of the form Cel = γT1.2, which is expected for massless Dirac fermion states in topological insulators, or spin-liquid phases

Studies of cracking behavior in melt-processed YBCO bulk superconductors

An important phenomenon in bulk superconductors fabricated by top-seeded-melt growth (TSMG) is the formation of cracks due to the inherent brittleness of the YBa2Cu3O7-δ (Y-123) phase matrix. These form during the fabrication of the superconducting monolith and play an important role in the limitation of current flow. However, cracks may also form during cooling cycles of the sample to liquid nitrogen temperatures. In this investigation, macrocracks along the c-direction, in particular were analyzed microscopically before and after cooling. In addition we attempt to resolve the c-axis macrocrack formation pattern using the magnetoscan technique

Crystal Structure and Physical Properties of U3T3Sn4 (T = Ni, Cu) Single-Crystals

Heat capacity experiments, crystal structure determination and transmission electron microscopy have been carried out on U3Cu3Sn4 single-crystals. U3Cu3Sn4 was confirmed to be a heavy-fermion antiferromagnet (TN=13(1) K) with a low temperature electronic heat capacity coefficient gamma=390 mJ/molUK2. Low temperature heat capacity experiments on a U3Ni3Sn4 single-crystal indicate that below 0.4 K there is a crossover between the previously observed non-Fermi liquid behavior and a Fermi liquid state.Comment: 12 pages (incl. 2 tables & 4 figures), to appear in Physica

Coexistence of Ferromagnetism and Unconventional Spin-Glass Freezing in the Site-Disordered Kagome Ferrite SrSn\u3csub\u3e2\u3c/sub\u3eFe\u3csub\u3e4\u3c/sub\u3eO\u3csub\u3e11\u3c/sub\u3e

Single-crystal x-ray diffraction refinements indicate SrSn2Fe4O11 crystallizes in the hexagonal R-type ferrite structure with noncentrosymmetric space group P63mc and lattice parameters a = 5.9541(2)Å, c = 13.5761(5)Å, Z = 2 (R(F) = 0.034). Octahedrally coordinated 2a [M(1) and M(1a)] and 6c sites [M(2)] have random, mixed occupation by Sn and Fe; whereas the tetrahedrally coordinated 2b sites [Fe(3) and Fe(3a)] are exclusively occupied by Fe, whose displacement from the ideal position with trigonal-bipyramidal coordination causes the loss of inversion symmetry. Our dc and ac magnetization data indicate SrSn2Fe4O11 single crystals undergo a ferro- or ferri-magnetic transition below a temperature TC = 630 K with very low coercive fields μoHc⊥ = 0.27 Oe and μoHc∥ = 1.5 Oe at 300 K, for applied field perpendicular and parallel to the c axis, respectively. The value for TC is exceptionally high, and the coercive fields exceptionally low, among the known R-type ferrites. Time-dependent dc magnetization and frequency-dependent ac magnetization data indicate the onset of short-range, spin-glass freezing below Tf = 35.8 K, which results from crystallographic disorder of magnetic Fe3+ and nonmagnetic Sn4+ ions on a frustrated Kagome sublattice. Anomalous ac susceptibility and thermomagnetic relaxation behavior in the short-range-ordered state differs from that of conventional spin glasses. Optical measurements in the ultraviolet to visible frequency range in a diffuse reflectance geometry indicate an overall optical band gap of 0.8 eV, consistent with observed semiconducting properties

Recovery of the Fermi-liquid state in U_3Ni_3Sn_4 by pressure

Measurements of the resistivity of single-crystalline U_3Ni_3Sn_4 under hydrostatic pressure up to 1.8 GPa are reported. We show that the temperature T_FL, below which the resistivity obeys the Fermi-liquid expression rho ~ T^2, increases with pressure as T_FL ~ (p-p_c)^1/2. The analysis of the data within the magnetotransport theory of Rosch lends strong support for an antiferromagnetic quantum critical point in U_3Ni_3Sn_4 at a negative critical pressure p_c of -0.04+-0.02 GPa. The proximity to an antiferromagnetic instability in U_3Ni_3Sn_4 is consistent with the previously reported non-Fermi liquid term in the low-temperature specific heat.Comment: 14 pages (including 4 figures); pdf forma

Studies of cracking behavior in melt-processed YBCO bulk superconductors

An important phenomenon in bulk superconductors fabricated by top-seeded-melt growth (TSMG) is the formation of cracks due to the inherent brittleness of the YBa2Cu3O7-δ (Y-123) phase matrix. These form during the fabrication of the superconducting monolith and play an important role in the limitation of current flow. However, cracks may also form during cooling cycles of the sample to liquid nitrogen temperatures. In this investigation, macrocracks along the c-direction, in particular were analyzed microscopically before and after cooling. In addition we attempt to resolve the c-axis macrocrack formation pattern using the magnetoscan technique

Myocardial remodeling and fibroblast growth factor in patients with resistant hypertension

Aim. To study the prevalence and severity of left ventricular hypertrophy (LVH), its relationship with fibroblast growth factor (FGF23) in patients with resistant hypertension (RH) depending on the effectiveness of multiagent antihypertensive therapy.Material and methods. The study included 92 patients diagnosed with RH. All patients underwent 24-hour ambulatory blood pressure monitoring (ABPM), echocardiography, general laboratory tests, and the serum FGF23 level was determined.Results. According to ABPM results, patients were divided into following groups: 1st — controlled RH (n=44) and 2nd — uncontrolled (n=48) RH. The groups were comparable in sex, age, main clinical and anthropometric parameters. In group 2, the main parameters of ABPM were higher. There were no differences in general laboratory tests, In the group of uncontrolled RH, the level of FGF23 was higher — 11,7 [8,5; 15,4] pmol/ml vs 9,2 [7,1; 11,6] pmol/ml in the 1st group (p=0,0036). According to echocardiography, a comparable violation of left ventricular (LV) diastolic function, an increase in left atrial size, LV mass (LVM) and LVM index were found. In patients of the 2nd group, large values of interventricular septal thickness were revealed — 1,3 [1,2; 1,4] cm vs 1,2 [1,1; 1,3] cm in the 1st group (p=0, 0043) and relative LV wall thickness (LVWT) — 0,50 [0,48; 0,53] vs, 0,45 [0,43; 0,50] in the 1st group (p<0,0001). In the 1st and 2nd groups, concentric LVH was more common (18 (41%) patients in the 1st and 26 (54,1%) in the 2nd (p=0,044) groups) than eccentric LVH (15 (34,1%) and 13 (27,1%) patients in the 1st and 2nd groups, respectively). Correlation analysis revealed a positive relationship between pulse pressure and HTN duration (r=48, p=0,02) and FGF23 level (r=0,62, p=0,004). The LVM index was positively associated with the diastolic pressure-time index (BP) (r=51, p=0,02). A positive correlation was found between relative LVWT and pulse pressure (r=0,64, p=0,02) and a negative relationship with the duration of regular antihypertensive therapy (r=47, p=0,04), A strong relationship was found between LVEF and FGF23 levels (r=0,75, p=0,005).Conclusion. For patients with uncontrolled resistant hypertension, an increase in pulse pressure and myocardial remodeling in the form of concentric hypertrophy are more characteristic. FGF23 is significantly higher in uncontrolled RH and is positively associated with pulse pressure and relative LVWT

The level of VEGF-A in the lacrimal fluid of diabetic retinopathy

The lacrimal fluid was investigated in 56 people (95 eyes) with type II diabetes, of which 11 (11 eyes) with no signs of diabetic retinopathy and 45 patients (84 eyes) suffering from diabetic retinopathy of varying severity. Investigation of VEGF-A (vascular endothelial growth factor A) in stimulated lacrimal fluid revealed its level in all patients. It was significantly higher in patients with diabetic retinopathy compared with data that have been obtained in patients with diabetes, but without signs of diabetic retinopathy. Statistically significant differences in the level of VEGF-A in patients with non-proliferative and proliferative retinopathy of 1-3 stages have not been identified. At the same time in patients with far-advanced retinopathy with marked variations of fatal retina and vitreous body (detachment expressed gliosis), but without evidence of neovascularization of the anterior eye, a significant decrease in the level of vasoproliferative factors has revealed

A Novel Magnetoscan Setup

Due to a modification in the original magnetoscan setup, a significant improvement in resolution was obtained. The paper focuses on experimental results which should support the idea of the new setup using two magnets with opposite direction of magnetization. This contribution to the characterization techniques of melt-grown bulk superconductors should promote the easy installation of this technique in industry. The improved magnetoscan technique may further help to investigate growth-induced inhomogeneities of the top-seeded-melt-growth process in the submillimeter range, and it offers new possibilities to the characterization of smaller structures such as superconducting films or coated conductors.Comment: 7 pages, 7 figure