received and accepted dates provided by the publisher other relevant dates provided by the publisher PACS 72.15.Gd -Galvanomagnetic and other magnetotransport effects PACS 78.70.Bj -Positron annihilation Abstract -Magneto resistance measurements coupled with positron lifetime measurements, to characterize the vacancy type defects, have been carried out on the topological insulator (TI) system Bi 2 Se 3, of varying Se/Bi ratio. Pronounced Shubnikov de Haas (SdH) oscillations are seen in nominal Bi 2 Se 3.1 crystals for measurements performed in magnetic fields up to 15 T in the 4 K to 10 K temperature range, with field applied perpendicular to the (001) plane of the crystal. The quantum oscillations, characteristic of 2D electronic structure, are seen only in the crystals that have a lower concentration of Se vacancies, as inferred from positron annihilation spectroscopy.

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ARTICLE This journal isIn this study we examine the phase transitions in single crystals of [(CH 3 ) 2 NH 2 ]Co(HCOO) 3 , using magnetization and specific heat measurements as a function of temperature and magnetic field. Magnetisation measurements indicate a transition at 15 K that is associated with an antiferromagnetic ordering. Isothermal magnetization versus magnetic field curves, demonstrate the presence of a singleion magnet phase, coexisting with antiferromagnetism. A peak in specific heat is seen at 15 K, corresponding to the magnetic transition and the enthalpy of the transition evaluated from the area under the specific heat peak decreases with the application of magnetic field of upto 8 T. This is suggestive of long range antiferromagnetic magnetic order, giving way to single-ion magnetic behavior under external magnetic field. At high temperatures, the specific heat measurements, shows a peak at ~155 K, that is insensitive to applied magnetic field. Raman scattering studies confirm the presence of structural transition. The magnetisation in this temperature range, while it exhibits a paramagnetic behavior, shows a distinct jump and the paramagnetic susceptibility changes across the structural transition.

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We report precision X-ray powder-diffraction (XRD) data of single phase pure Ti2ZrAl. Ti2ZrAl samples were prepared by an arc melting method and annealed at 1000 °C for 30 days. XRD analysis was carried out on these samples and it was found that Ti2ZrAl has a DO19 structure (space group P63/mmc, No. 194). The lattice parameters are found to be a=5.961±0.001 Å and c=4.793±0.001 Å.