Reentrant Spin-Peierls Transition in Mg-Doped CuGeO_3

We report a synchrotron x-ray scattering study of the diluted spin-Peierls (SP) material Cu_{1-x}Mg_xGeO_3. In a recent paper we have shown that the SP dimerization attains long-range order only for x < x_c = 0.022(0.001). Here we report that the SP transition is reentrant in the vicinity of the critical concentration x_c. This is manifested by broadening of the SP dimerization superlattice peaks below the reentrance temperature, T_r, which may mean either the complete loss of the long-range SP order or the development of a short-range ordered component within the long-range ordered SP state. Marked hysteresis and very large relaxation times are found in the samples with Mg concentrations in the vicinity of x_c. The reentrant transition is likely related to the competing Neel transition which occurs at a temperature similar to T_r. We argue that impurity-induced competing interchain interactions play an essential role in these phenomena.Comment: 5 pages, 4 embedded eps figure

On a q-difference Painlev\'e III equation: II. Rational solutions

Rational solutions for a $q$-difference analogue of the Painlev\'e III equation are considered. A Determinant formula of Jacobi-Trudi type for the solutions is constructed.Comment: Archive version is already official. Published by JNMP at http://www.sm.luth.se/math/JNMP

Thermal conductivity of Mg-doped CuGeO_3 at very low temperatures: Heat conduction by antiferromagnetic magnons

Thermal conductivity \kappa is measured at very low temperatures down to 0.28 K for pure and Mg-doped CuGeO_3 single crystals. The doped samples carry larger amount of heat than the pure sample at the lowest temperature. This is because antiferromagnetic magnons appear in the doped samples and are responsible for the additional heat conductivity, while \kappa of the pure sample represents phonon conductivity at such low temperatures. The maximum energy of the magnon is estimated to be much lower than the spin-Peierls-gap energy. The result presents the first example that \kappa at very low temperatures probes the magnon transport in disorder-induced antiferromagnetic phase of spin-gap systems

Structural Critical Scattering Study of Mg-Doped CuGeO3

We report a synchrotron x-ray scattering study of the diluted spin-Peierls (SP) material Cu_(1-x)Mg_xGeO_3. We find that for x>0 the temperature T_m at which the spin gap is established is significantly higher than the temperature T_s at which the SP dimerization attains long-range order. The latter is observed only for xx_c the SP correlation length quickly decreases with increasing x. We argue that impurity-induced competing interactions play a central role in these phenomena.Comment: 5 pages, 4 embedded eps figures, to appear in PR

Two-stage spin-flop transitions in S = 1/2 antiferromagnetic spin chain BaCu_2Si_2O_7

Two-stage spin-flop transitions are observed the in quasi-one-dimensional antiferromagnet, BaCu${}_2$Si${}_2$O${}_7$. A magnetic field applied along the easy axis induces a spin-flop transition at 2.0 T followed by a second transition at 4.9 T. The magnetic susceptibility indicates the presence of Dzyaloshinskii-Moriya (DM) antisymmetric interactions between the intrachain neighboring spins. We discuss a possible mechanism whereby the geometrical competition between DM and interchain interactions, as discussed for the two-dimensional antiferromagnet La${}_2$CuO${}_4$, causes the two-stage spin-flop transitions.Comment: 5 pages, 3 figures (included), accepted for publication in Phys. Rev. Let

The first-order phase transition between dimerized-antiferromagnetic and uniform-antiferromagnetic phases in Cu_(1-x)M_xGeO_3

We have performed detailed magnetic susceptibility measurements as well as synchrotron x-ray diffraction studies to determine the temperature vs concentration ($T$ - $x$) phase diagram of Cu${}_{1-x}$Mg${}_x$GeO${}_3$. We observe clear double peaks in the magnetic susceptibility implying two antiferromagnetic (AF) transition temperatures in samples with Mg concentrations in the range 0.0237 $\le x \le$ 0.0271. We also observe a drastic change in the inverse correlation length in this concentration range by x-ray diffraction. The drastic change of the AF transition temperature as well as the disappearance of the spin-Peierls (SP) phase have been clarified; these results are consistent with a first-order phase transition between dimerized AF (D-AF) and uniform AF (U-AF) phases as reported by T. Masuda {\it et al.} \lbrack Phys. Rev. Lett. {\bf 80}, 4566 (1998)\rbrack. The $T$ - $x$ phase diagram of Cu${}_{1-x}$Zn${}_x$GeO${}_3$ is similar to that of Cu${}_{1-x}$Mg${}_x$GeO${}_3$, which suggests that the present phase transition is universal for Cu${}_{1-x}M_{x}$GeO${}_3$.Comment: 7 pages, 5 figures. submitted to PR

Clinical use and efficacy of biphasic insulin lispro 50/50 in people with insulin treated diabetes-A nationwide evaluation of clinical practice

© 2015 Informa UK Ltd. Objectives: This study aims to investigate the metabolic effects of biphasic insulin lispro 50/50 in routine clinical practice. A total of 229 patients who were 18 years old with diabetes, newly treated with biphasic insulin lispro 50/50, were sourced from six secondary care services in England. Methods: Detailed clinical parameters were compared at baseline, and 3 and 6 months post-initiation. Responders was defined as those with HbA1c 1% (11mmol/mol) at 6 months. Results: HbA1c showed significant reduction:-0.93% (-10mmol/mol) and-1.2% (-13mmol/mol) at 3 and 6 months respectively, while no significant change was noted for all the other parameters. When analyzed according to frequencies of injections/day, the greatest reduction was observed with the three times a day regimen (-1.0% [-11.0mmol/mol] and-1.3% [-14.6mmol/mol] at 3 and 6 months respectively). HbA1c reduction was greatest in the group who previously received a basal-bolus insulin regimen: (-0.8% [-9.0mmol/mol] and-1.5% [-16.2mmol/mol] at 3 and 6 months respectively). Reduction in weight was observed at 3 months (-1.8kg±4.3) only for those who were previously on a basal-bolus insulin regimen. Insulin doses increased following conversion to biphasic insulin lispro 50/50, irrespective of the types of insulin used prior to biphasic insulin lispro 50/50, but this was not associated with weight gain. The independent predictors of response to biphasic insulin lispro 50/50 were baseline HbA1c, Caucasian, presence of nephropathy, prior use of basal-bolus insulin and prior use of other premixed combination. Conclusion: Biphasic insulin lispro 50/50 is therefore an effective therapeutic option for achieving glycemic control in patients with suboptimal HbA1c levels, especially among those who were previously on a basal-bolus insulin regimen and those who received it three times daily, with a neutral effect on weight parameters. Limitations: This was a retrospective study of routine clinical practice and is therefore limited by allocation bias and some missing data. Information on rates of hypoglycemia and quality of life are not available

Weak ferromagnetism of quasi-one-dimensional S=1/2 antiferromagnet BaCu2_2Ge2_2O7_7

Weak ferromagnetism of quasi-one-dimensional S = 1/2 antiferromagnet BaCu$_2$Ge$_2$O$_7$ is studied by the magnetization measurement. The spontaneous magnetization appears along the b axis. The local symmetry between the in-chain nearest neighbor spins allows the presence of Dzyaloshinskii-Moriya interaction, and the only possible spatial configuration of the weak ferromagnetic moment per spin determines the sign of the inter-chain interaction. A weak $a$-axis magnetic field can change the direction of the magnetization to the $a$-axis direction, which shows that the spin chain forms a weakly coupled weak-ferromagnetic chain system.Comment: 10 pages, 4 figure