Phase transitions in LaFeAsO: structural, magnetic, elastic, and transport properties, heat capacity and Mossbauer spectra

We present results from a detailed experimental investigation of LaFeAsO, the parent material in the series of "FeAs" based oxypnictide superconductors. Upon cooling this material undergoes a tetragonal-orthorhombic crystallographic phase transition at ~160 K followed closely by an antiferromagnetic ordering near 145 K. Analysis of these phase transitions using temperature dependent powder X-ray and neutron diffraction measurements is presented. A magnetic moment of ~0.35 Bohr magnetons per iron is derived from Mossbauer spectra in the low temperature phase. Evidence of the structural transition is observed at temperatures well above the structural transition (up to near 200 K) in the diffraction data as well as the polycrystalline elastic moduli probed by resonant ultrasound spectroscopy measurements. The effects of the two phase transitions on the transport properties (resistivity, thermal conductivity, Seebeck coefficient, Hall coefficient), heat capacity, and magnetization of LaFeAsO are also reported, including a dramatic increase in the magnitude of the Hall coefficient below 160 K. The results suggest that the structural distortion leads to a localization of carriers on Fe, producing small local magnetic moments which subsequently order antiferromagnetically upon further cooling. Evidence of strong electron-phonon interactions in the high-temperature tetragonal phase is also observed.Comment: Revised and expanded magnetization and Mossbauer spectroscopy section. Clarified sample preparation description. This paper contains some results from arXiv:0804.0796. 10 figure

Solanum trilobatum in the management of atopy: Through inhibition of mast cell degranulation and moderation of release of interleukins

Solanum trilobatum is a widely used plant in the Indian indigenous systems of medicine. It is mainly used in the treatment of respiratory diseases like bronchial asthma. In our present study, we report that the aqueous and alcoholic extracts of S. trilobatum exhibited inhibition of mast cell degranulation. Further, aqueous and alcoholic extracts of S. trilobatum significantly decreased the release of IL1α and increased the release of IL8 from the cultured keratinocytes. Oral administration of the aqueous and alcoholic extracts of S. trilobatum stabilized mast cells in experimental rats