School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan 689-798, Republic of Korea.
Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University , Suwon 440-746, Republic of Korea.
ACS Nano. 2016 Apr 26;10(4):4618-26. doi: 10.1021/acsnano.6b00921. Epub 2016 Mar 14.
Electrical control of ferromagnetism in semiconductor nanostructures offers the promise of nonvolatile functionality in future semiconductor spintronics. Here, we demonstrate a dramatic gate-induced change of ferromagnetism in ZnO nanowire (NW) field-effect transistors (FETs). Ferromagnetism in our ZnO NWs arose from oxygen vacancies, which constitute deep levels hosting unpaired electron spins. The magnetic transition temperature of the studied ZnO NWs was estimated to be well above room temperature. The in situ UV confocal photoluminescence (PL) study confirmed oxygen vacancy mediated ferromagnetism in the studied ZnO NW FET devices. Both the estimated carrier concentration and temperature-dependent conductivity reveal the studied ZnO NWs are at the crossover of the metal-insulator transition. In particular, gate-induced modulation of the carrier concentration in the ZnO NW FET significantly alters carrier-mediated exchange interactions, which causes even inversion of magnetoresistance (MR) from negative to positive values. Upon sweeping the gate bias from -40 to +50 V, the MRs estimated at 2 K and 2 T were changed from -11.3% to +4.1%. Detailed analysis on the gate-dependent MR behavior clearly showed enhanced spin splitting energy with increasing carrier concentration. Gate-voltage-dependent PL spectra of an individual NW device confirmed the localization of oxygen vacancy-induced spins, indicating that gate-tunable indirect exchange coupling between localized magnetic moments played an important role in the remarkable change of the MR.
半导体纳米结构中的铁磁体的电控制有望在未来的半导体自旋电子学中实现非易失性功能。在这里，我们展示了在 ZnO 纳米线（NW）场效应晶体管（FET）中，磁场显著的栅极诱导变化。我们 ZnO NWs 中的铁磁性来自于氧空位，它构成了容纳不成对电子自旋的深能级。所研究的 ZnO NWs 的磁转变温度估计远高于室温。原位 UV 共聚焦光致发光（PL）研究证实了所研究的 ZnO NW FET 器件中的氧空位介导的铁磁性。估计的载流子浓度和温度相关的电导率都表明所研究的 ZnO NW 处于金属-绝缘体转变的交叉点。特别是，在 ZnO NW FET 中栅极诱导的载流子浓度调制显著改变了载流子介导的交换相互作用，这甚至导致磁电阻（MR）从负到正的反转。当栅极偏压从-40V 扫到+50V 时，在 2K 和 2T 下估计的 MR 从-11.3%变为+4.1%。对栅极依赖的 MR 行为的详细分析清楚地表明，随着载流子浓度的增加，自旋分裂能增强。单个 NW 器件的栅极依赖 PL 光谱证实了氧空位诱导自旋的局域化，表明局域磁矩之间的栅极可调间接交换耦合在 MR 的显著变化中起着重要作用。
