Frustrated spin-1/2 square lattice in the layered perovskite PbVO(3)

We report on the magnetic properties of the layered perovskite PbVO(3). The results of magnetic susceptibility and specific heat measurements as well as band structure calculations consistently suggest that the S=1/2 square lattice of vanadium atoms in PbVO(3) is strongly frustrated due to next-nearest-neighbor antiferromagnetic interactions. The ratio of next-nearest-neighbor (J(2)) to nearest-neighbor (J(1)) exchange integrals is estimated to be J(2)/J(1)\approx 0.2-0.4. Thus, PbVO(3) is within or close to the critical region of the J(1)-J(2) frustrated square lattice. Supporting this, no sign of long-range magnetic ordering was found down to 1.8 K.Comment: 4 pages, 4 figures, 2 table

Emergent helical texture of electric dipoles

Long-range ordering of magnetic dipoles in bulk materials gives rise to a broad range of magnetic structures, from simple collinear ferromagnets and antiferromagnets, to complex magnetic helicoidal textures stabilized by competing exchange interactions. In contrast, in the context of dipolar order in dielectric crystals, only parallel (ferroelectric) and antiparallel (antiferroelectric) collinear alignments of electric dipoles are typically considered. Here, we report an observation of incommensurate helical ordering of electric dipoles by light hole-doping of the quadruple perovskite BiMn7O12. In analogy with magnetism, the electric dipole helicoidal texture is also stabilized by competing instabilities. Specifically, orbital ordering and lone electron pair stereochemical activity compete, giving rise to phase transitions from a non-chiral cubic structure, to an incommensurate electric dipole and orbital helix, via an intermediate density wave

Unusual effects of magnetic dilution in the ferrimagnetic columnar ordered Sm2MnMnMn4−xTixO12\mathrm{Sm_2MnMnMn_{4-x}Ti_xO_{12}} perovskites

Powder neutron diffraction experiments have been employed to establish the effects of site-selective magnetic dilution in the Sm2MnMnMn4-x Tix O12 A-site columnar ordered quadruple perovskite manganites (x = 1, x = 2 and x = 3). We show that in all three compositions the Mn ions adopt a collinear ferrimagnetic structure below 27 K, 62 K and 34 K, respectively. An unexpected increase in the ordering temperature was observed between the x = 1 and x = 2 samples, which indicates a considerable departure from mean field behaviour. This result is corroborated by large reductions in the theoretical ground state magnetic moments observed across the series, which indicate the presence of spin fluctuations and or disorder. We show that long range magnetic order in the x = 3 sample, which occurs below the percolation threshold for B-B exchange, can only be understood to arise if magnetic order in Sm2MnMnMn4-xTixO12 is mediated via both A-B and B-B exchange, hence confirming the importance of A-B exchange interactions in these materials. Finally we show that site-selective magnetic dilution enables the tuning of a ferrimagnetic compensation point and the introduction of temperature-induced magnetization reversal.Comment: 10 pages, 7 figure

Crystal and magnetic structure transitions in bimno3+δ ceramics driven by cation vacancies and temperature

The crystal structure of BiMnO$_{3+δ}$ ceramics has been studied as a function of nominal oxygen excess and temperature using synchrotron and neutron powder diffraction, magnetometry and differential scanning calorimetry. Increase in oxygen excess leads to the structural transformations from the monoclinic structure (C2/c) to another monoclinic (P2$_{1}$/c), and then to the orthorhombic (Pnma) structure through the two-phase regions. The sequence of the structural transformations is accompanied by a modification of the orbital ordering followed by its disruption. Modification of the orbital order leads to a rearrangement of the magnetic structure of the compounds from the long-range ferromagnetic to a mixed magnetic state with antiferromagnetic clusters coexistent in a ferromagnetic matrix followed by a frustration of the long-range magnetic order. Temperature increase causes the structural transition to the nonpolar orthorhombic phase regardless of the structural state at room temperature; the orbital order is destroyed in compounds BiMnO$_{3+δ}$ (δ ≤ 0.14) at temperatures above 470 °C

The role of newly diagnosed diabetes mellitus for poor in-hospital prognosis of coronary artery bypass grafting

Background: The management of coronary artery disease in patients with type 2 diabetes (T2DM) who need myocardial revascularization is a great challenge. Aims: To study the role of newly diagnosed T2DM in the development of in-hospital adverse outcomes after coronary artery surgery (CABG). Methods: 708 consecutive patients underwent CABG were included. All patients without history of T2DM and with border fasting hyperglycemia underwent an oral glucose tolerance test. Results: The screening allowed to diagnose T2DM in 8.9% and prediabetes in 10.4% of the study population. The the number of patients with T2DM increased from 15.2% to 24.1%, and with prediabetes from 3.0% to 13.4%. The total number of patients with carbohydrate metabolism disorders increased from 18.2% to 37.5%. The trend towards higher rate of in-hospital complications after CABG was defined among patients with newly diagnosed and previously diagnosed T2DM. The regression analysis demonstrated the presence of the relationships between the previously diagnosed T2DM and the total number of significant complications (odds ratio (OR) 1.350, 95% confidence interval (CI): 1.0571.723, p=0.020) and prolonged in-hospital stay (OR 1.609, 95%CI 1.2022.155, p=0.001). The significance of these relationships increased with the addition of newly diagnosed T2DM to the regression model (for in-hospital complications: OR 1.731, 95% CI 1.1312.626, p=0.012; for prolonged in-hospital stay: OR 2.229, 95%CI 1.4123.519, p0.001). Moreover, additional associations between T2DM and the risk of developing multiple organ dysfunction (OR 2.911, 95% CI 1.0727.901, p=0.039), urgent lower extremity surgery (OR 1.638, 95%CI 1.00915.213, p=0.020) and the need for extracorporeal correction of hemostasis (OR 3.472, 95%CI 1.04211.556, p=0.044) have been defined. Importantly, the presence of these associations would not have been identified without including newly diagnosed DM in the regression model. Conclusion: The newly diagnosed T2DM affects the prognosis of CABG as well as the previously diagnosed T2DM. The obtained results suggest the importance of active preoperative T2DM screening