Study of the electrical and magnetic properties of the superconducting FeSe_0.5Te_0.5

Full text: Since the discovery of superconductivity at a transition temperature Tc = 26 K in LaFeAsO_1-xF_x, several types of Fe-based superconductors, essentially composed of 2-dimensional Fe-square lattices, have been discovered [1]. Among the iron-based superconductors, FeSe_1-x has the simplest structure. The superconducting transition temperature (T_C) of 8 K was found to dramatically increase under pressure reaching a maximum of 37 K [2]. Additionally, it was observed that an applied pressure changes the electronics phase diagram and induces magnetic order which can coexist with superconductivity. FeSe_0.5Te_0.5 samples were produced by self-flow method. Appropriate amounts of powdered iron (99%), tellurium (99.997%) and selenium (99.99%) were mixed and pressed into pellets. The pellets were sealed in quartz ampoules under vacuum. The ampoules were heated to 600 °C and kept at this temperature for 12 hours and then fired to 930 °C for 24 hours. After, the material was cooled to a temperature of 400 °C at a rate of 5 °C / h and was finally subjected to rapid cooling in water at room temperature. We have studied the physical properties of iron-chalcogenide FeSe_0.5Te_0.5. X-ray diffraction for samples was performed at room temperature. Rietveld analysis of XRD patterns were performed using the GSAS program. We have found that the crystalline parameters are in agreement with those reported in the literature [3]. We also carried out measurements of the electrical resistivity and micrographs were taken on a scanning electron microscopy. Complementary magnetic characterizations were also performed. References: [1] Kamihara Y., Watanabe T., Hirano M. and Hosono H., J. Am. Chem. Soc., 130 (2008) 3296. [2] Margadonna, S., Takabayashi, Y., Ohishi, Y., Mizuguchi, Y., Takano, Y., Kagayama, T., Nakagawa, T., Takata, M., and Prassides, K. Pressure evolution of the low-temperature crystal structure and bonding of the superconductor FeSe (T= 37K). Phys. Rev. B 80 (Aug 2009), 064506. [3] Yeh, K.-W., Huang, T.-W., Lin Huang, Y., Chen, T.-K., Hsu, F.-C., Wu, P. M., Lee, Y.-C., Chu, Y.-Y., Chen, C.-L., Luo, J.-Y., Yan, D.-C., And Wu, M.-K. Tellurium substitution effect on superconductivity of the α-phase iron selenide. EPL (Europhysics Letters) 84, 3 (2008), 37002. (author)