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

Epitaxial ZnO thin films co-doped with 3d transition metal (TM) (TM = Cr, M n, Fe, Co, Ni and Cu) and 1 mol% Al were fabricated as a series of oxide-di luted magnetic semiconductors by pulsed-laser-deposition method. Magnetores istance (MR) of the films was measured to investigate the s-d exchange inte raction between the conducting s electron spins and the d electron spins lo calized at the magnetic TM impurities. A variety of MR behaviors were obser ved depending on the different TM impurities. It is deduced that the negati ve MR behavior in the vicinity of zero held is originated from an electron weak-localization effect. Caused by the s-d exchange interaction, the incre ase of Thomas-Fermi radius R, and the decrease of spin-disorder scattering with increasingly aligned spins of the TM ion impurities are responsible re spectively for the positive and negative MR in the higher magnetic filed. ( C) 2001 Elsevier Science B.V. All rights reserved.