Paramagnetism and conductivity in nanostructured Bi-Sr-Ca-Cu-O

Abstract

On nanocrystalline materials, which were grown by an appropriate annealing of quasi-amorphous Bi 2 Sr 2 CaCu 2 O 8+δ , the static magnetic susceptibility χ and electrical conductivity σ have been measured between 1.8 and 300 K. Up to grain sizes of d c = 50 nm, the crystalline phase displays the Bi 2 Sr 2 CuO 6+δ (Bi2201) structure. Upon increasing size of the Bi2201 nanocrystals, an onset of a variable-range-hopping type σ (T ) is observed along with a rapid reduction of χ which comprises contributions from both the Curie term and the temperature-independent background. We propose to associate these novel features with the depletion of the intergranular phase, containing rather large amounts of paramagnetic centres and of antiferromagnetically coupled pairs, at the expense of the formation of metallic 2201-nanocrystals.

Magnetic phase diagram of the layered superconductor Bi2+xSr2−xCuO6+δ(Bi2201) withTc≈ 7 K

“…For all curves we used the same criterium, by selecting the normal state region that produced the best fit. It should be mentioned that a similar normal state background with a small linear temperature dependence term was previously observed in Bi2201 nanocristaline-phase [12]. As shown in the curves of Fig.…”

“…For all curves we used the same criterion, by selecting the normal state region that produced the best fit. It should be mentioned that a similar normal state background with a small linear temperature dependence term was previously observed in Bi2201 nanocrystalline phase [12]. As shown in the curves of figure 1, the resulting isofield M(T) curves show a large reversible region displaying a linear region with T, followed by a pronounced rounding effect as magnetization approaches zero, which is reminiscent of superconducting fluctuations in the vicinity of T c (H) in high-T c superconductors [13][14][15][16].…”