Order-disorder transition in Bi2.1Sr1.9CaCu2O8 + delta single crystals doped with Fe and Pb
This article was originally published as: Uprety, KK, Horvat, J, Wang, XL, Ionescu, M, Liu, HK, Dou, SX, & Brandt, EH, Order-disorder transition in Bi2.1Sr1.9CaCu2O8 + delta single crystals doped with Fe and Pb, Physical review - Series B, 2002, 65, 224501 (7 pages), and may be found here. Copyright 2002 American Physical Society.
The magnetic field Hdis(T) where an order-disorder transition of the vortex lattice in high-Tc superconductors occurs, is investigated by measurements of the magnetization M(H) in Bi2.1Sr1.9CaCu2O8 + delta (Bi2212) single crystals doped with iron and lead. Comparative studies are made of the temperature dependences of the field Hpeak(T), where the second peak occurs in |M(H)|, and the fields Hmin(T), and Hinfl(T) where a minimum and an inflection point occur at the low-field side of this peak. It is proposed that Hdis(T) lies close to Hinfl. In Bi2.1Sr1.9Ca1.0(Cu1–yFey)2O8 + delta single crystals with Fe concentration y = 0, 0.005, 0.016, and 0.022, a pronounced peak in the derivative |dM/dH| is observed, whose position Hinfl(T) is independent of temperature T. We relate this peak to the field Hdis(T), which separates a weakly elastically disordered vortex lattice from a plastically disordered vortex solid. In heavily Pb-doped single Bi2212 crystals, Hinfl(T) decreases with increasing T. For the same crystals, a minimum in the normalized relaxation rate S(H) is observed at Hinfl, indicating two different flux-creep mechanisms above and below that field and two different solid vortex phases. It is argued that the negative slope of Hdis(T) in heavily-Pb-doped Bi2212 crystals is related to the enhanced c axis conductivity caused by the Pb sitting between the CuO2 layers and causing three-dimensional vortex lines, while in Fe-doped Bi2212 crystals the Fe ions sit on the CuO2 planes and thus do not enhance the coupling between pancake vortices.
K. K. Uprety, J. Horvat, X. L. Wang, M. Ionescu, H. K. Liu, S. X. Dou, and E. H. Brandt. "Order-disorder transition in Bi2.1Sr1.9CaCu2O8 + delta single crystals doped with Fe and Pb" Faculty of Engineering - Papers (2002).
Available at: http://works.bepress.com/sxdou/43