基于半金属Co2MnSi/Ag/Co2MnSi自旋阀器件的自旋电子注入与检测

The high efficient injecton,manipulation and detection of the electron angular momentum is very important to spintronics which may have a profound impact on spin devices. As a new electronical detection technique, non-local electronic structure has attracted much attention since it can produce pure spin current which inhibit some charge-related spurious effects. Many experiments have been carried out to detect spin accumulation signals by non-local electronic structure. But so far, only metal electrodes such as Fe, Co, NiFe et al. have been used to inject spin electrons into metals or semiconductors. Due to the high Curie temperature (985 K),good chemical ordering of L21 structure and large spin polarization which is about 100% in theory, half-metallic Heusler Co2MnSi alloy can be used as the ferromagnets to prepare Co2MnSi/Ag/Co2MnSi lateral spin valve structure. Here, we will use non-local detection technique to measure the spin accumulation signals based on Co2MnSi/Ag/Co2MnSi spin valve. By optimizing the preparation parameters of Co2MnSi film and lateral spin valves, we hope to increase the spin polarization of devices, enhance the spin diffusion length in Ag material and get much obvious spin accumulation signals. The carrying out of the project will not only open another way for the choice of present electrode materials, but also check the interior physical mechanism of the change of spin resistance, spin polarization and spin diffusion length. It will help to find new electrode materials and improve the current research on spin injection and spin detection.

把自旋电子高效注入到非磁金属中，操控并检测自旋电子是实现自旋电子器件最基本的条件。但是迄今为止，只有磁性金属材料如Fe、Co、NiFe等被用做注入与检测电极材料，自旋极化率有待提高。本项目提出采用半金属Co2MnSi做为自旋阀的注入与检测电极材料，金属Ag做为非磁性材料制备自旋阀器件，采用非局域法测量器件的自旋聚集信号。通过优化Co2MnSi的沉积速率、退火温度、退火时间等制备参数，得到具有良好L21结构的Co2MnSi薄膜；通过优化Co2MnSi线、Ag线的曝光时间、显影时间、刻蚀时间等工艺参数，得到电学性能稳定的自旋阀器件。通过测得更明显的自旋聚集信号，从而在实验上验证Co2MnSi电极材料的采用能够增强电子的自旋极化率，提高电子在金属Ag中的自旋扩散长度。该项目的开展不仅为电极材料的选用提供有益的参考，而且能探索自旋信号变化的影响因素与物理机制，将对自旋注入与检测的研究起到推动作用。

本项目重点研究了：(a) Co-Mn-Si原子成分比；(b) Co-Mn-Si沉积速率；(c) 退火时间、退火温度对Co-Mn-Si薄膜有序度、剩余电阻比、磁阻尼系数以及各向异性磁电阻的影响。制备得到了高取向的Co-Mn-Si薄膜，薄膜高的剩余电阻比、低的磁阻尼系数以及负的各向异性磁电阻表明其具有优良的半金属性。采用半金属Co2MnSi电极，本项目制作了Co2MnSi/Ag/Co2MnSi 自旋阀。通过改变微加工过程中的曝光时间、显影时间、刻蚀时间、丙酮去胶时间等工艺参数以保证Co2MnSi/Ag界面清晰洁净，Co2MnSi线、Ag线结构完整，成功的制作了可用于非局域测量的自旋阀器件，并检测到了明显的自旋电阻。我们制作的Co2MnSi/Ag/Co2MnSi器件中，Ag的自旋扩散长度长度达到了290纳米，Co2MnSi的自旋极化率为74 %。以上结果表明，采用半金属Co2MnSi电极做为自旋注入与检测器件中的铁磁电极，能够促进自旋电子的非平衡聚集，得到大的自旋扩散长度。此外，本项目还通过改变成分原子比、溶液PH值、退火温度、退火时间等制备工艺参数，制备出了具有一定B2取向度、磁性能较好的半金属Co-Fe-Al纳米Heusler颗粒。该结果表明，利用简单、成本低廉的化学共沉淀法制备Heusler材料是完全可行的。