Magnetoresistance of 3d transition metal single-doped and co-doped epitaxial ZnO thin films

Magnetoresistance (MR) of transition metal (TM)-doped and co-doped ZnO films prepared by a magnetron sputtering system has been discussed. For single-doped film, the values of Hmax (the field at which MR shows its maximum) increase as temperature increases. At a certain temperature, the values of Hmax increase from Mn-, Fe- to Co-doped films due to their different magnetic moments. For (Mn, Fe), (Mn, Co)-co-doped ZnO films, the MR behaviors show striking similarity as Mn-doped ZnO film. These results are interpreted in terms of the s-d spin-splitting mechanism. Large negative MR in high field is attributed to the formation of magnetic polarons (MPs). The temperature dependence of resistivity agrees well with the variable range hopping (VRH) mechanism of MPs.