量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.
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Graphene/ferromagnet heterostructures are receiving an intensive interest due to the expectation of both improving the existing storage devices and paving the way for the next generation of memory technologies with higher speed and lower power consumption. The long spin diffusion length in graphene originated from the weak spin-orbit interaction and high electron mobility has stimulated numerous studies on developing graphene-based lateral spin valves (SV) in the past decade [1]. Apart from the application to lateral SV dealing with in-plane spin transportation in a graphene channel, another potential application that is the implementation of graphene as a spacer material in vertical SV has recently become a subject of intense interest [2]. Up to now, the ferromagnets involved in the graphene/ferromagnet heterostructures are limited to the conventional magnetic materials with low spin-polarization, which corresponds for the poor performance found in those graphene/ferromagnet heterostructures based spintronic devices.
In order to improve the performance of graphene/ferromagnet based spintronic devices, we recently developed a novel heterostructure which consists of a single layer graphene (SLG) on a full Heusler alloy CoFeGe0.5Ga0.5 (CFGG) ferromagnet with high-polarization [3], by in-situ chemical vapor deposition and magnetron-sputtering technique. The growth of high-quality with a full coverage of SLG on CFGG was succeeded by careful optimization of the growth procedure. The spin-resolved electronic properties of the interface region in the SLG/CFGG heterostructure were examined by depth-resolved x-ray magnetic circular dichroism spectroscopy with atomic depth resolution. It is revealed that the SLG/CFGG heterostructure shows not only a quasi-free-standing nature of SLG but also a robust magnetism comparable to that of bulk one in the atomic layer adjacent to SLG. In addition, the density functional theory calculation results indicate the linear Dirac band structure of graphene and half-metallicity of CFGG in the vicinity of the interface are well preserved in the SLG/CFGG heterostructure. The unusual preservation of the inherent electronic and magnetic properties at the SLG/CFGG interface is associated with the weak van der Waals interactions at the interface, which differs from other reported graphene/ferromagnet heterostructures where a strong interfacial interaction of chemical bonding was usually observed. The possibility of using this newly developed SLG/CFGG heterostructure for realizing high-performance graphene spintronic devices will be also discussed.
A Novel Graphene/Heusler Alloy Heterostructure for Advanced Spintronic Device Application
