Structural, Magnetic, Magnetocaloric, and Magnetostrictive Properties of Pb_1-xSr_xMnBO₄(x = 0, 0.5, and 1.0)

The solid solution Pb1-xSrxMnBO4 is reported with an orthorhombic, Pnma, structure throughout; here studies on compounds with x = 0, 0.5 and 1 are described. The structure contains chains of MnO6 octahedra that exhibit intra-chain ferromagnetic (FM) order at low temperatures. Neutron powder diffraction (NPD) reveals dominant FM order in PbMnBO4 (Tc = 30 K), whereas SrMnBO4 is primarily antiferromagnetic (AFM) with TN = 16 K; the difference is related to the link between the chains that involves the BO3 groups. PbMnBO4 has its moment along a but also has a previously unreported AFM contribution along c (magnetic space group Pnm'a'), whereas SrMnBO4 has its moment along a but also a FM canting along c (magnetic space group Pn'm'a). The end members show distinct magnetostriction at Tc/TN which correlates with the different magnetic exchange in these compounds. NPD in variable applied magnetic field shows that SrMnBO4 is converted to fully FM at 8 T. The behavior above the magnetic ordering temperature is consistent with short-range FM correlations within the chains, which is particularly apparent in PbMnBO4. The magnetocaloric effect (MCE) has been measured and compared with those previously reported for the mineral gaudefroyite. PbMnBO4 has excellent MCE behavior, especially near Tc, 30 K. The strong FM exchange within the chains and FM correlations above Tc are vital for the MC properties

Nodal s± pairing symmetry in an iron-based superconductor with only hole pockets

The origin of high-temperature superconductivity in iron-based superconductors is still not understood; determination of the pairing symmetry is essential for understanding the superconductivity mechanism. In the iron-based superconductors that have hole pockets around the Brillouin zone centre and electron pockets around the zone corners, the pairing symmetry is generally considered to be s±, which indicates a sign change in the superconducting gap between the hole and electron pockets. For the iron-based superconductors with only hole pockets, however, a couple of pairing scenarios have been proposed, but the exact symmetry is still controversial. Here we determine that the pairing symmetry in KFe2As2—which is a prototypical iron-based superconductor with hole pockets both around the zone centre and around the zone corners—is also of the s± type. Our laser-based angle-resolved photoemission measurements have determined the superconducting gap distribution and identified the locations of the gap nodes on all the Fermi surfaces around the zone centres and the zone corners. These results unify the pairing symmetry in hole-doped iron-based superconductors and point to spin fluctuation as the pairing glue in generating superconductivity

<i>Trans</i>-vaccenic acid reprograms CD8⁺ T cells and anti-tumour immunity

Diet-derived nutrients are inextricably linked to human physiology by providing energy and biosynthetic building blocks and by functioning as regulatory molecules. However, the mechanisms by which circulating nutrients in the human body influence specific physiological processes remain largely unknown. Here we use a blood nutrient compound library-based screening approach to demonstrate that dietary trans-vaccenic acid (TVA) directly promotes effector CD8+ T cell function and anti-tumour immunity in vivo. TVA is the predominant form of trans-fatty acids enriched in human milk, but the human body cannot produce TVA endogenously. Circulating TVA in humans is mainly from ruminant-derived foods including beef, lamb and dairy products such as milk and butter, but only around 19% or 12% of dietary TVA is converted to rumenic acid by humans or mice, respectively. Mechanistically, TVA inactivates the cell-surface receptor GPR43, an immunomodulatory G protein-coupled receptor activated by its short-chain fatty acid ligands. TVA thus antagonizes the short-chain fatty acid agonists of GPR43, leading to activation of the cAMP–PKA–CREB axis for enhanced CD8+ T cell function. These findings reveal that diet-derived TVA represents a mechanism for host-extrinsic reprogramming of CD8+ T cells as opposed to the intrahost gut microbiota-derived short-chain fatty acids. TVA thus has translational potential for the treatment of tumours

On the Anionic Group Approximation to the Borate Nonlinear Optical Materials

In this mini-review type of article, a brief summary of the anionic group approximation as it relates to the borate nonlinear optical (NLO) crystals, an idea firstly proposed by Professor Chen, is presented.The basic idea, calculation method, tabulated coefficients of various common borate, as well as nitrate or carbonate groups, in their ideal geometries will be presented. New practices reveal that those parameters can still give very accurate predicted NLO coefficients for recently found NLO crystals without any adjustment of parameters

On the Anionic Group Approximation to the Borate Nonlinear Optical Materials

In this mini-review type of article, a brief summary of the anionic group approximation as it relates to the borate nonlinear optical (NLO) crystals, an idea firstly proposed by Professor Chen, is presented.The basic idea, calculation method, tabulated coefficients of various common borate, as well as nitrate or carbonate groups, in their ideal geometries will be presented. New practices reveal that those parameters can still give very accurate predicted NLO coefficients for recently found NLO crystals without any adjustment of parameters

Synthesis, structure and property studies of a new series of rare earth (Ce, Tb) bismuth silicates

A new series of rare earth bismuth silicates has been synthesized by flux method and solid state reaction. LnBiSiO5 (Ln = Ce, Tb) crystallizes in a triclinic space group P-1 with cell parameters a = 5.6763(2) angstrom, alpha = 105.591(3)degrees b = 6.7922(3) angstrom, beta = 110.551(3)degrees c = 6.9593(2) angstrom, gamma = 99.733(3) degrees, Z = 2. They exhibit a novel three-dimensional structure consisting of zig-zag chains of edge-sharing Ce/TbO8 polyhedra that are further linked by SiO4 units and Bi2O8 clusters. The optical band gap (E-g) of TbBiSiO5 was estimated to be 3.84 eV from UV-Vis-IR diffuse reflectance spectra. Photoluminescence measurements suggest that due to the cooperative interaction of Bi and Tb the excitation bands monitored at 544 nm are shifted towards longer wavelength which may favor commercial UV diode excitation. The magnetic measurements show that TbBiSiO5 exhibits paramagnetic behavior without magnetic transitions down to 1.8 K