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Spin-polarized graphene for low-power electronics

    A research team led by Professor Ariando from the National University of Singapore (NUS) have developed a technique allowing to both induce and measure spin polarization in a system consisting of graphene and a ferrimagnetic oxide insulator. In their paper published on December 6 2023 in Advance Materials, they detail how they have been able to experimentally achieve a large tunability along with a high degree of polarization in graphene, enabling new advances and possibilities in the field of two-dimensional (2D) spintronics.

    Graphene is a well-known 2D material that has been the object of extensive studies, both theoretical and experimental, since its discovery in 2004. Such atomically thin material can help to manipulate and control the spin of electrons throughout their strong spin-orbit coupling and high carrier mobility. Although graphene does not carry spin polarization, it has long spin lifetime and diffusion length at room temperature, making it a material of choice for spintronics.

    This figure illustrates the diffusion of spin-polarized electrons in a graphene layer on top of the ferrimagnetic insulating oxide (TmIG). The strong exchange interaction between the graphene and TmIG leads to a significant spin-splitting in the graphene’s band structure. As a result, this splitting causes a marked disparity in the density of charge carriers with spin up and down orientations. This disparity in carrier density is responsible for the creation of a spin-polarized current. Credit: NUS.

    The chosen substrate is a ferrimagnetic insulating oxide: Tm3Fe5O12 (TmIG), its insulating property leaves graphene as the only transport channel in the system and its perpendicular magnetic anisotropy induces a strong exchange coupling with graphene. Thin films of TmIG were epitaxially grown on (111)-oriented substituted gadolinium gallium garnet (SGGG) as described in the figure above.

    Spin polarization in graphene is induced through interface exchange interaction between TmIG and graphene, triggered by the proximity of the two layers. Such magnetic proximity effect (MPE) leads to spin-dependent transport in magnetized graphene and results in a spin-splitting energy. In order to directly quantify the spin splitting-energy, Professor Ariando’s research team have developed an innovative method using the Landau fan shift. Proximity effects between graphene and TmIG leads to a spin splitting term in the Landau levels of spin-polarized graphene, which can be evaluated by probing the oscillation frequency derived from the slope of the Landau fan diagram. Those results were fitted using machine learning computation. In addition, it is important to note that field cooling allows to tune the spin-splitting energies, such that they were able to tune it over a range between 98 and 166 meV.

    “Our work develops a robust and unique route to generate, detect and manipulate the spin of electrons in atomically thin materials.”, Professor Ariando said. “It also demonstrates a practical use of artificial intelligence in materials science. With the rapid development and significant interest in the field of 2D magnets and stacking-induced magnetism in atomically thin van der Waals heterostructures, we believe our results can be extended to various other 2D magnetic systems.”

    More information: Magnetic graphene for low-power electronics | EurekAlert! (November 2023)

    Original article: Tunable Spin‐Polarized States in Graphene on a Ferrimagnetic Oxide Insulator – Hu – 2023 – Advanced Materials – Wiley Online Library