Periodic Reporting for period 1 - GRISOTO (GRaphene-Interfaced heterostructures for Spin Orbit TOrques)
Reporting period: 2020-05-01 to 2022-04-30
This project aimed at combining materials exhibiting two-dimensional transport for the generation of spin-orbit torques (SOT). We stacked graphene (which possesses very large electronic mobility) on top of materials with large spin-orbit coupling (SOC). Making use of the proximity effect, the close contact of both materials allows for the conversion from charge to spin current. Such conversion is useful for the manipulation of the magnetization of a contiguous ferromagnetic layer (FM), using SOT, a promising mechanism for next-generation magnetic memories.
The chosen SOC-materials were 2D transition metal dichalcogenides (TMD, such as MoS2 or WS2) and topological insulators (TI, with bulk insulating behavior and topologically-protected conductive surface states). Preparation of such SOC-material/graphene/FM heterostructures was carried out, in particular focusing on the optimization of the graphene/TI interface. Characterization of the interface proved that the insertion of graphene prevented both the oxidation at the surface of the TI and the intermixing with a ferromagnetic layer (permalloy, Py) grown on top. Coplanar waveguides and Hall bars were patterned from the aforementioned heterostructures and spin-torque ferromagnetic resonance measurements were carried out to study the spin-to-charge conversion efficiency. New insights about the system were gained and reported.
The chosen SOC-materials were 2D transition metal dichalcogenides (TMD, such as MoS2 or WS2) and topological insulators (TI, with bulk insulating behavior and topologically-protected conductive surface states). Preparation of such SOC-material/graphene/FM heterostructures was carried out, in particular focusing on the optimization of the graphene/TI interface. Characterization of the interface proved that the insertion of graphene prevented both the oxidation at the surface of the TI and the intermixing with a ferromagnetic layer (permalloy, Py) grown on top. Coplanar waveguides and Hall bars were patterned from the aforementioned heterostructures and spin-torque ferromagnetic resonance measurements were carried out to study the spin-to-charge conversion efficiency. New insights about the system were gained and reported.
Work performed and overview of the results: Heterostructures of materials with large spin-orbit coupling and 2D transport/graphene/ferromagnet (permalloy) were prepared. Significant efforts were focused on the optimization of graphene/topological insulator interfaces, achieved by transferring CVD-grown graphene on top of the topological insulator film (grown by molecular beam epitaxy) under inert atmosphere. Optimization of such procedure and characterization of the obtained interfaces and heterostructures showed that graphene capping successfully passivates the topological insulator surface, thus protecting it from oxidation after posterior air exposure, as well as preventing interdiffusion when the permalloy is grown on top to obtain the final heterostructure. These final heterostructures were patterned and spin-torque ferromagnetic resonance was performed in order to analyze the spin-orbit torques of such stacks. The interpretation of the final results is still ongoing.
Exploitation and dissemination: the results of this project were presented in a poster in an online conference (2020) and in an oral presentation in a conference in Grenoble (2021). Two publications in scientific journals have reviewed the current state of the art in of spin-to-charge conversion in 2D materials, other publication(s) with the specific results of the project are expected in the near future. Outreach talks were also carried out to promote science at schools, increasing the visibility of women in science.
Exploitation and dissemination: the results of this project were presented in a poster in an online conference (2020) and in an oral presentation in a conference in Grenoble (2021). Two publications in scientific journals have reviewed the current state of the art in of spin-to-charge conversion in 2D materials, other publication(s) with the specific results of the project are expected in the near future. Outreach talks were also carried out to promote science at schools, increasing the visibility of women in science.
Spin-orbit torques (SOT) are currently considered a promising method for the next generation of MRAMs, and the use of two-dimensional materials in heterostructures for such SOT (as studied during this project) offers great promise even if is still at its infancy. This project has been a step forward in the exploration of materials towards optimization of this SOT and understanding of the proximity effect phenomena, contributing to the unlocking of next-generation devices such as memories based on the exploitation of spin-orbit coupling.
From a material science point of view, the introduction of graphene at the interface has also proven to be advantageous, allowing for the passivation of the underlying topological insulator layers and preventing intermixing, which is typically present in TI/FM heterostructures and leads to the suppression of SOTs.
Furthermore, through a series of outreach activities, a large number of youngsters were exposed to the relevance of nanotechnologies and science at large, where women can contribute side by side with men.
From a material science point of view, the introduction of graphene at the interface has also proven to be advantageous, allowing for the passivation of the underlying topological insulator layers and preventing intermixing, which is typically present in TI/FM heterostructures and leads to the suppression of SOTs.
Furthermore, through a series of outreach activities, a large number of youngsters were exposed to the relevance of nanotechnologies and science at large, where women can contribute side by side with men.