Naval Research Laboratory , Code 7130, Washington, DC 20375, United States.
ACS Nano. 2016 Apr 26;10(4):4857-62. doi: 10.1021/acsnano.6b01982. Epub 2016 Apr 14.
We provide evidence that magnetic moments formed when hydrogen atoms are covalently bound to graphene exhibit spin glass ordering. We observe logarithmic time-dependent relaxations in the remnant magnetoresistance following magnetic field sweeps, as well as strong variances in the remnant magnetoresistance following field-cooled and zero-field-cooled scenarios, which are hallmarks of canonical spin glasses and provide experimental evidence for the hydrogenated graphene spin glass state. Following magnetic field sweeps, and over a relaxation period of several minutes, we measure changes in the resistivity that are more than 3 orders of magnitude larger than what has previously been reported for a two-dimensional spin glass. Magnetotransport measurements at the Dirac point, and as a function of hydrogen concentration, demonstrate that the spin glass state is observable as the zero-field resistivity reaches a value close to the quantum unit h/2e(2), corresponding to the point at which the system undergoes a transition from weak to strong localization. Our work sheds light on the critical magnetic-dopant density required to observe spin glass formation in two-dimensional systems. These findings have implications to the basic understanding of spin glasses as well the fields of two-dimensional magnetic materials and spintronics.
我们提供的证据表明，当氢原子通过共价键与石墨烯结合时，会形成磁矩，这些磁矩表现出自旋玻璃有序。我们观察到磁场扫描后残余磁电阻的对数时间依赖性弛豫，以及磁场冷却和零场冷却情况下残余磁电阻的强烈方差，这些都是典型自旋玻璃的特征，并为氢化石墨烯的自旋玻璃态提供了实验证据。在磁场扫描之后，经过几分钟的弛豫期，我们测量到的电阻率变化超过了以前报道的二维自旋玻璃的 3 个数量级。在狄拉克点的磁输运测量以及随氢浓度的变化，证明自旋玻璃态是可观察到的，因为零场电阻率接近量子单位 h/2e(2)，这对应于系统从弱局域到强局域的转变点。我们的工作揭示了在二维系统中观察到自旋玻璃形成所需的临界磁掺杂密度。这些发现对于理解自旋玻璃以及二维磁性材料和自旋电子学领域具有重要意义。
