Phung Thu Thi, Nguyen Mai Thi, Pham Lien Thi, Ngo Lan Thi, Nguyen Tung Thanh
Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Vietnam.
University of Science and Technology of Hanoi, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Ha Noi, Vietnam.
J Phys Condens Matter. 2022 Jun 10;34(31). doi: 10.1088/1361-648X/ac742a.
In this work, the magnetic states and thermally induced spin currents in graphene nanoflake sizes with different sizes and shapes have been investigated using Hubbard model combined with non-equilibrium Green's function method. In addition to the antiferromagnetic (AFM) state governed by the sizes, shapes, armchair bond densities, and Coulomb energy, our calculations have also pointed out the emergence of ferromagnetic (FM) and complex magnetic states when the gate voltage is invoked in the graphene nanoflakes. More prominently, by exploiting the geometric symmetry of the nanoflakes without external fields, a pure spin current and zero charge current are generated in spin caloritronic device when the graphene nanoflakes are both in the AFM and FM states. The formation of pure spin currents driven by temperature difference depends on the graphene nanoflakes' size, shape, temperature and gate voltage as well. The study also shows the outstanding advantages of diamond-shaped graphene nanoflakes in both magnetic properties and spin currents. This result paves the way for the possibility of practical applications of graphene materials in spintronics and spin caloritronics.
在这项工作中，我们结合哈伯德模型和非平衡格林函数方法，研究了不同尺寸和形状的石墨烯纳米片的磁态和热致自旋电流。除了受尺寸、形状、扶手椅键密度和库仑能支配的反铁磁（AFM）态外，我们的计算还指出，当在石墨烯纳米片中施加栅极电压时，会出现铁磁（FM）态和复杂磁态。更突出的是，通过利用无外场时纳米片的几何对称性，当石墨烯纳米片处于AFM态和FM态时，自旋热电器件中会产生纯自旋电流和零电荷电流。由温差驱动的纯自旋电流的形成也取决于石墨烯纳米片的尺寸、形状、温度和栅极电压。该研究还展示了菱形石墨烯纳米片在磁性能和自旋电流方面的突出优势。这一结果为石墨烯材料在自旋电子学和自旋热电子学中的实际应用可能性铺平了道路。
