Spin-related magnetoresistance of n-type ZnO:Al and Zn1-xMnxO:Al thin films

Effects of spin-orbit and s-d exchange interactions are probed by magnetoresistance (MR) measurements carried out down to 50mK on ZnO and Zn1-xMnxO with x=3 and 7% and electron concentration ∼1020cm-3. A description of the data for ZnO:Al in terms of weak-localization theory leads to the coupling constant λso=(4.4±0.4)×10-11eVcm of the kp hamiltonian for the wurzite structure, Hso=λsoc(s×k). A complex and large MR of Zn1-xMnxO:Al is interpreted in terms of the influence of the s-d spin-splitting on the disorder-modified electron-electron interactions, which explains positive MR. A large negative MR is tentatively assigned to a precursor effect of the magnetic polaron formation. It is suggested that the proposed model explains the origin of MR observed recently in many magnetic oxide systems.