Temperature dependence of enhanced spin relaxation time in metallic nanoparticles: Experiment and theory
Temperature dependence of enhanced spin relaxation time in metallic nanoparticles: Experiment and theory
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金属纳米颗粒中增强的自旋弛豫时间的温度依赖性：实验和理论
DOI：
10.1103/physrevb.93.085402
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
and K. Takanashi
中科院分区：
文献类型：
--
作者：
T. Koda;S. Mitani;S. Takahashi;M. Mizuguchi;K. Sato;T. J. Konno;S. Maekawa;and K. Takanashi
研究了Fe/MgO/Au纳米颗粒/MgO/Fe堆叠结构纳米柱双势垒结器件中Au纳米颗粒的自旋弛豫时间增强效应。位于电流路径中的Au纳米颗粒的尺寸从透射电子显微照片和器件的电流-电压特性中的库仑阻塞行为推导出。在临界电流以上观察到有限的隧道磁电阻（TMR），这归因于Au纳米颗粒中的自旋积累。基于一个简单的TMR模型，由于自旋积累在纳米粒子，自旋弛豫时间估计的幅度的临界电流。从系统的观测中确定了TMR出现的温度和偏置电压区域，表明TMR的出现与库仑阻塞无关，而是与自旋积累有关。我们发现，所获得的是在低温下延长（约800 ns），并突然下降超过临界温度。有趣的是，临界温度强烈地依赖于Au纳米颗粒的尺寸，并且远低于对应于离散能量间距的有效温度。对具有分立能级的电子自旋弛豫的理论分析表明，电子自旋弛豫时间的显著延长和电子自旋弛豫时间的强烈温度依赖性都是由于与周围基体中声子的耦合引起的分立能级的展宽引起的。使用合理的参数值的数值计算很好地再现所观察到的温度和尺寸依赖性的自旋弛豫时间在Au纳米粒子。
We study the enhanced spin relaxation time of Au nanoparticles in nanopillar-shaped double-barrier junction devices with a stacked Fe/MgO/Au-nanoparticle/MgO/Fe structure. The size of Au nanoparticles located in a current path is deduced from a transmission electron micrograph and the Coulomb blockade behavior in the current-voltage characteristics of the devices. A finite tunnel magnetoresistance (TMR) is observed above a critical current and is attributable to spin accumulation in Au nanoparticles. Based on a simple model of TMR due to spin accumulation in a nanoparticle, the spin relaxation timeis estimated from the magnitude of the critical current. The temperature and bias-voltage region where TMR appears are determined from systematic observations, showing that the appearance of TMR is not associated with the Coulomb blockade but with spin accumulation. We find that the obtainedis anomalously extended (∼800 ns) at low temperatures and abruptly decreases above a critical temperature. Interestingly, the critical temperature strongly depends on the size of the Au nanoparticles and is much lower than the effective temperature corresponding to the discrete energy spacing. A theoretical analysis for the spin relaxation of electrons with discrete energy levels shows that not only the anomalously extended spin relaxation time, but also the strong temperature dependence ofarise from thebroadeningof discrete energy levels due to coupling with phonons in the surrounding matrix. Numerical calculations using reasonable parameter values well reproduce the observed temperature and size dependence of the spin relaxation time in Au nanoparticles.