Magnetoresistance and Hall effect near the metal-insulator transition ofn-typeCd0.95Mn0.05Te

The magnetoresistance (MR) and Hall coefficient of n-type ${\mathrm{Cd}}_{0.95}$ ${\mathrm{Mn}}_{0.05}$Te samples with carrier concentrations 1.2×${10}^{17}$≤n≤6.6×${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}3}$ 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 ${\mathit{n}}_{\mathit{c}}$≃2×${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}3}$, in rough agreement with Mott’s prediction. In fields H≲80 kOe the resistivity ρ first increases with H, then passes through a maximum, and finally decreases. The increase of ρ at low fields is accompanied by an increase in the magnitude of the Hall coefficient, while the decrease of ρ 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 ρ at low fields follows the behavior expected from quantum corrections to the conductivity arising from the electron-electron interaction. The decrease of ρ 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<${\mathit{n}}_{\mathit{c}}$ 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>${\mathit{n}}_{\mathit{c}}$) the MR and Hall coefficient exhibit oscillations at high fields. The oscillations are interpreted as Shubnikov–de Haas oscillations arising from the majority-spin subband. This interpretation is supported by model calculations.