Magnetoresistance in n-type conducting Co-doped ZnO

Series of Co-doped Al-codoped ZnO films with electron concentration at 5 K ranging from 8.31017 cm-3 to 9.91019 cm-3 were prepared by pulsed laser deposition under different O2 pressure and substrate temperature. The magnetoresistance (MR) effect was studied between 5 K and 290 K with fields up to 6 T, showing large electron concentration and temperature dependence. A large positive MR of 124 % has been observed in the film with the lowest electron concentration of 8.31017 cm-3, while only negative MR of –1.9 % was observed in the film with an electron concentration of 9.91019 cm-3 at 5 K. The positive MR is attributed to the quantum correction on the conductivity due to the s-d exchange interaction induced spin-splitting of the conduction band [1]. The negative MR is attributed to the magnetic field suppressed weak localization [1]. The modelled superimposed positive and negative MR agrees well with the experimentally observed MR and hints towards the physical origin of MR in Co-doped ZnO [2].
[1] P. A. Lee and T. V. Ramakrishnan, Rev. Mod. Phys. 57, 287 (1985)
[2] Q. Xu, L. Hartmann, H. Schmidt, H. Hochmuth, M. Lorenz, D. Spemann, and M. Grundmann, Phys. Rev. B 76, 134417 (2007)