Weak ferromagnetism in normal state Bi2Sr2CaCu2O8+d nano-superconductors
Superconducting nano powders Bi2Sr2CaCu2O8+d (Bi-2212) was synthesized using a wet mixing method, where all the basic material is completely dissolved using HNO3 solution. The basic ingredients were Bi2O3, SrCO3, CaCO3, and CuO. The PbO2 was also used as dopants to produce powder Bi2-xPbxSr2CaCu2O8+d [(Bi,Pb)-2212]. After being dissolved completely in HNO3, the mixture with thoroughly stoichiometric calculation to produce the 2212 phase was then stirred while heated for drying. These results were then heated gradually at temperatures of calcination and sintering in a short duration, in order to make 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.