Spin-related magnetoresistance of n-type ZnO:Al and Zn1-xMnxO:Al thin films -: art. no. 121309

Effects of spin-orbit and s-d exchange interactions are probed by magnetoresistance (MR) measurements carried out down to 50 mK on ZnO and Zn1-xMnxO with x=3 and 7% and electron concentration similar to 10(20) cm(-3). A description of the data for ZnO:Al in terms of weak-localization theory leads to the coupling constant lambda(so)=(4.4 +/- 0.4)x10(-11) eV cm of the kp hamiltonian for the wurzite structure, H-so=lambda(so)c(sxk). 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.