MAGNETORESISTANCE AND HALL-EFFECT NEAR THE METAL-INSULATOR-TRANSITION OF N-TYPE CD0.95MN0.05TE

The magnetoresistance (MR) and Hall coefficient of n-type Cd0.95Mn0.05Te samples with carrier concentrations 1.2×1017*n*6.6×1017 cm-3 were measured at 1.2*T*4.2 K in fields up to 200 kOe. The results at zero magnetic field show that the carrier concentration at the metal-insulator transition is nc2×1017 cm-3, in rough agreement with Motts prediction. In fields H80 kOe the resistivity first increases with H, then passes through a maximum, and finally decreases. The increase of at low fields is accompanied by an increase in the magnitude of the Hall coefficient, while the decrease of above the maximum is accompanied by an increase in the Hall mobility. The MR below 80 kOe is attributed to mechanisms associated with the giant spin splitting of the conduction band. The increase of at low fields follows the behavior expected from quantum corrections to the conductivity arising from the electron-electron interaction. The decrease of above the maximum is attributed to the rise of the Fermi energy in the majority-spin subband. Above 80 kOe the qualitative behavior of the MR depends on the carrier concentration. Samples with n<nc exhibit an upturn in the resistivity at high fields. This effect is attributed to the squeezing of the donor-electron wave function. In addition, the MR of these samples shows an anomaly near the first magnetization step. In metallic samples (n>nc) the MR and Hall coefficient exhibit oscillations at high fields. The oscillations are interpreted as Shubnikovde Haas oscillations arising from the majority-spin subband. This interpretation is supported by model calculations. © 1990 The American Physical Society.