Spin-on Spintronics : Ultrafast Electron Spin Dynamics in ZnO and Zn1-xCoxO Sol-Gel Films

We use time-resolved Faraday rotation spectroscopy to probe the electron spin dynamics in ZnO and magnetically doped Zn1-xCoxO sol-gel thin films. In undoped ZnO, we observe an anomalous temperature dependence of the ensemble spin dephasing time T2*, i.e., longer coherence times at higher temperatures, reaching T2* ∼ 1.2 ns at room temperature. Time-resolved transmission measurements suggest that this effect arises from hole trapping at grain surfaces. Deliberate addition of Co2+ to ZnO increases the effective electron Landé g factor, providing the first direct determination of the mean-field electron-Co2+ exchange energy in Zn1-xCoxO (N0alpha = +0.25 (0.02 eV). In Zn1-xCoxO, T2* also increases with increasing temperature,allowing spin precession to be observed even at room temperature