S. Moehlecke

Ferromagnetic- and Superconducting-Like Behavior of Graphite

We have identified ferromagnetic- and superconducting-like magnetization hysteresis loops in highly oriented pyrolytic graphite samples below and above room temperature. We also found that both behaviors are very sensitive to low-temperature—as compared to the sample synthesis temperature—heat treatment. The possible contribution of magnetic impurities and why these do not appear to be the reason for the observed phenomena is discussed.

Landau Level Quantization and Possible Superconducting Instabilities in Highly Oriented Pyrolitic Graphite

Measurements of the basal-plane resistivity ρa(T,H) performed on highly oriented pyrolitic graphite, with magnetic field H∥c-axis in the temperature interval 2–300K and fields up to 8 T, provide evidence for the occurrence of both field-induced and zero-field superconducting instabilities. Additionally, magnetization M(T,H) measurements suggest the occurrence of Fermi surface instabilities which compete with the superconducting correlations.

Inhomogeneous superconductivity in Bi2Sr2Ca1-xPrxCu2O8+δ

Abstract We have studied Pr doping effect on the superconducting transition temperature onset T C ( x ) in Bi 2 Sr 2 Ca 1− x Pr x Cu 2 O 8+ δ superconducting polycrystalline samples by means of both resistance R ( T , x ) and magnetization M ( T , x ) measurements. It is found that while the resistively determined T CR ( x ) rapidly decreases with x for x >0.4, the T CM ≈85 K obtained from magnetization measurements remains unchanged. We argue that the suppression of T CR ( x ) is related to the reduction of the sample superconducting volume fraction which ultimately leads to disconnected superconducting clusters. Resistive behavior measured at different applied currents in a sample close to percolation threshold supports this discussion.

Universal magnetic-field-driven metal-insulator-metal transformations in graphite and bismuth

Applied magnetic field induces metal-insulator and reentrant insulator-metal transitions in both graphite and rhombohedral bismuth. The corresponding transition boundaries plotted on the magnetic field\char22{}temperature

Magnetic field dependent quantum flux creep in Bi2Sr2Ca2Cu3O10

(B\text{\ensuremath{-}}T)

Enhancement of the intergranular superconducting properties in Bi2Sr2CaCu2O8 with Li additions

plane nearly coincide for these semimetals and can be best described by power laws

Interaction between superconducting and ferromagnetic order parameters in graphite-sulfur composites

T\ensuremath{\sim}{(B\text{\ensuremath{-}}{B}_{c})}^{\ensuremath{\kappa}}

Thermomagnetic Flux-Jump Instabilities and Second Magnetization Peak in Bi2Sr2CaCu2O8 High-Tc Superconducting Crystals

, where

Long-time temperature drift in a commercial SQUID magnetometer

{B}_{c}

Possible electrical-current-driven superconductor-insulator transition

is a critical field at