Weak ferromagnetism in the normal state of Bi2Sr2CaCu2O8+d nano-superconductors
Superconducting Bi2Sr2CaCu2O8+d (Bi-2212) nanoparticles were successfully synthesized using a wet mixing method, where all the starting materials were completely dissolved in HNO3 solution. The basic ingredients were Bi2O3, SrCO3, CaCO3, and CuO. The PbO2 was also introduced as dopant to prepare Bi2-xPbxSr2CaCu2O8+d [(Bi,Pb)-2212] powder. After being mixed and dissolved completely in HNO3, the mixture with thoroughly stoichiometric calculation to produce the 2212 phase was then stirred while heated for drying. The samples were then heated gradually at temperatures of calcination and sintering in a short duration, in order to produce nano-powders containing 2212 phase having crystal size less than 100 nm.
The TEM image of Bi-2212 powders, where the powder size of < 100 nm is seen.
(a) The critical temperature (Tc) of Bi-2212 samples sintered for 8 hours and (Bi, Pb) -2212 sintered for 4 hours;
(b) hysteresis curve at 80 K and 300 K for Bi-2212 samples were sintered for 8 hours, exhibiting a weakly ferromagnetic behavior in the normal state (above Tc).