The s-d exchange model as the underlying mechanism of magnetoresistance in ZnO doped with alkali metals.

High field magnetoresistance has been studied in epitaxial n-type ZnO:Na and ZnO:Li thin films in a temperature range between 4 K and 150 K. The resulting negative magnetoresistance can be well fitted using a semiempirical model of Khosla and Fischer based on third order contributions to the s-d exchange Hamiltonian. The parameters obtained from this model were carefully analyzed. One of these parameters is related to a ratio between electron mobilities at zero field (a non-exchange scattering mobility [Formula: see text] and an exchange or spin dependent one [Formula: see text]). From Hall effect measurements [Formula: see text] was obtained, displaying a weak temperature dependence in accordance with highly n-doped ZnO while the extracted [Formula: see text] exhibits an anomalous T-dependence. On the other hand, our magnetoresistance data cannot be properly fitted using Kawabata's expression based on a weak-localization model.