Change from electronlike to holelike carriers in MgCNi3 via doping with B or Zn

Hall coefficient RH has been studied systematically in normal state MgC1−xBxNi3 (x = 0.05, 0.15, 0.20) and Mg1−yZnyCNi3 (y = 0, 0.75, 1.00). It is found that RH changes from negative to positive while increasing B content x from 0.15 to 0.20. For x = 0.20, the sample still shows a superconducting transition at TC ∼ 4.5 K. RH is negative for MgCNi3 and positive for ZnCNi3. The absolute value |RH| for MgCNi3 decreases with the temperature increasing above ∼150 K, whereas |RH| for ZnCNi3 increases with the temperature increasing from 4 K to 300 K. For Mg0.25Zn0.75CNi3, RH changes from positive to negative when decreasing temperature to ∼205 K. These results confirm the two-band model, which indicates that electronlike and holelike carriers are coexisting in MgCNi3 system.