Magnetoresistance in laser-deposited Zn1–xCoxO thin films

We have measured the temperature and magnetic field dependence of the magnetoresistance (MR) in a series of laser-deposited Zn1-xCoxO (x = 0.02-0.25) thin films doped with 1 mol% Al. Three different MR behaviors are observed depending on the concentration of magnetic Co ions. The Zn1-xCoxO:Al film shows a giant positive MR as high as #~60% in 70 kOe at 5 K for x = 0.20. The observed MR features are discussed in terms of weak localization, s-d exchange coupling between the conducting carriers and localized spins of Co ions, and spin-disorder scattering.