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

2011 
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 Lande g factor, providing the first direct determination of the mean-field electron-Co2+ exchange energy in Zn1–xCoxO (N0α = +0.25 ± 0.02 eV). In Zn1–xCoxO, T2* also increases with increasing temperature, allowing spin precession to be observed even at room temperature.
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