Department of Physics and Center for Applied Photonics, University of Konstanz , D-78464 Konstanz, Germany.
Nano Lett. 2011 Aug 10;11(8):3355-60. doi: 10.1021/nl201736p. Epub 2011 Jul 19.
We use time-resolved Faraday rotation spectroscopy to probe the electron spin dynamics in ZnO and magnetically doped Zn(1-x)Co(x)O sol-gel thin films. In undoped ZnO, we observe an anomalous temperature dependence of the ensemble spin dephasing time T(2), i.e., longer coherence times at higher temperatures, reaching T(2) ∼ 1.2 ns at room temperature. Time-resolved transmission measurements suggest that this effect arises from hole trapping at grain surfaces. Deliberate addition of Co(2+) to ZnO increases the effective electron Landé g factor, providing the first direct determination of the mean-field electron-Co(2+) exchange energy in Zn(1-x)Co(x)O (N(0)α = +0.25 ± 0.02 eV). In Zn(1-x)Co(x)O, T(2) also increases with increasing temperature, allowing spin precession to be observed even at room temperature.
我们使用时间分辨的法拉第旋转光谱来探测 ZnO 和磁性掺杂 Zn(1-x)Co(x)O 溶胶-凝胶薄膜中的电子自旋动力学。在未掺杂的 ZnO 中，我们观察到电子自旋退相时间 T(2)的异常温度依赖性，即在较高温度下具有更长的相干时间，在室温下达到 T(2) ∼ 1.2 ns。时间分辨透射测量表明，这种效应源于晶粒表面的空穴捕获。故意添加 Co(2+)到 ZnO 中会增加有效电子朗德 g 因子，从而首次直接确定 Zn(1-x)Co(x)O 中的平均场电子-Co(2+)交换能（N(0)α = +0.25 ± 0.02 eV）。在 Zn(1-x)Co(x)O 中，T(2)也随温度升高而增加，甚至在室温下也可以观察到自旋进动。
