This work was supported by the National Science Foundation of China under Grant No. 50372052, 50430137, 50588201; the National Basic Research Program of China (973 program), under Grant No. 2007CB616906);the Program for Changjiang Scholars and Innovative Research Team in University;Australian Research Council under Grant No. DP0559872, DP0881739.
Single phase polycrystalline samples Na0.7Co1-xAlxO2 (x = 0, 0.05, 0.10, 0.15, 0.20, 0.25, 030) were prepared by solid state reaction. The magnetic properties from 5 K to 300 K have been studied by dc and ac magneti...