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Title: Tailoring spin-dependent transport in graphene-based hybrid devices
Speaker: Nga Thi Do (지도교수: 김태희 교수님)
Time and location: Nov. 30th (Wed) 5 PM, Science building AB101

Abstract

Spin-orbit coupling (SOC) is a crucial effect that plays a key role in manipulating the degree of freedom of electrons to be used for the information process of next-generation 2D spintronic devices. The tunability of SOC in spintronic materials, especially in 2D materials such as graphene, becomes very important for realizing innovative quantum devices [1]. However, tuning SOC in graphene-based heterostructures has remained a non-trivial task, and difficulties in controlling this phenomenon at industrial scale.

In this work, we focused on the interplay between Gr and Pt layers by inserting an ultrathin Co defect. As the Co thickness increases from 0.05 to 2.5 nm in Pt/Gr/SiO₂/Si(100) perpendicular stacks, different magnetoresistance behaviors have been observed in the intermediate temperature range (77-300K). The Co films were prepared on the wafer-scale CVD-grown Gr multilayers, and covered with a 3-nm-thick Pt using the UHV-Molecular Beam Epitaxy (MBE) film deposition technique. For the transport measurement, Pt-Hall bar devices were also prepared using the in-situ shadow mask patterning technique in the same UHV-MBE chamber. Our results showed that the quantum interference effect could be observed even at 77 K for the samples with a magnetic defect thickness of less than 0.2 nm. Notably, for the sample with 0.05-nm-thick Co, the WL-WAL crossover was clearly shown in the perpendicular MR measured at 77 K. To explore in more detail the Co-interlayer effects on the transport properties at the Pt/Gr interface, a theoretical analysis was performed using the modified Hikami-Larkin-Nagaoka (HLN) equation [2]. The interface properties were carefully analyzed for microstructural characterization of the heterostructures using AFM and HR-TEM.

Our results provide further insights into the transport phenomena and highlight the defect engineering of 2D-material with other ferromagnetic materials to manipulate and develop highly effective spintronic devices with new functionalities.

[References]

[1]. D. Pesin, D. & A. MacDonald, Spintronics and pseudospintronics in graphene and topological insulators, Nature Mater. 11, 409–416 (2012)

[2]. Shinobu Hikami, Anatoly I. Larkin, & Yosuke Nagaoka, Spin-Orbit Interaction and Magnetoresistance in the Two Dimensional Random System, Prog. Theor. Phys. 63, 707-710 (1980).