Two-Dimensional Spintronics

Identification of pure-spin signals in the voltage response of nanoscale structures has become a major direction in spintronics research during the last few years. Spin pumping has been demonstrated in FM/semiconductor interfaces (e.g., GaAs and p-type Si). Our group reported the first experimental evidence of spin pumping in FM/graphene (FM/Gr) interfaces (see references below). Graphene, a two-dimensional layer of carbon atoms, has unique electronic properties (e.g., high mobility and gate-tunable charge carrier density, among others), and stands as an excellent material for spin transport due to its large intrinsic spin coherence length. In fact, it has been proposed that hydrogenated graphene and chemical vapor deposition (CVD) graphene possess an enhanced spin-orbit coupling induced by H and Cu adatoms, respectively. We have observed this enhancement in ferromagnetic resonance (FMR) studies of FM/CVD-graphene interfaces, which may also explain the short spin relaxation rates previously observed in this material. As a matter of fact, the spin-orbit coupling in these graphene variants appears to be stronger than in heavy metals with substantial SHE angles (e.g., Pt). Note that the SHE in Pt and beta-Tantalum has been recently used to reversibly switch the magnetization of extended ferromagnetic films, opening the door to memory units entirely based on pure spin currents. In addition, in hydrogenated and CVD graphene it is possible to tune the density of carriers by applying local gate voltages (see figure above). These features make graphene-based pure spin current valves excellent candidates for the next generation of highly efficient information processing and storage units.

In this project we propose to perform a series of studies aimed at understanding and controlling the injection of pure spin currents in graphene-based spintronics devices through dynamical spin pumping and the spin-Hall effect. The proposed devices make use of the unique properties of graphene to allow for the generation and manipulation of pure spin currents, which will be employed to control the magnetic state of the device to an extent not possible with spin valves that use non-gateable spacers to separate the FM layers.

Recent Reference of this topic:

S. Singh, A. Ahmadi, C.T. Cherian, E. R. Mucciolo, E. del Barco, and B. Özyilmaz
“Dynamical spin injection at a quasi-one-dimensional ferromagnet-graphene interface”
Appl. Phys. Lett. 106, 032411 (2015)

S. Singh, Ph-D Thesis, UCF (2014).

S. Singh, D. Markó, E. del Barco and B. Özyilmaz.
“Spin pumping at Permalloy/graphene interface”
SPIE 8813, 88132O-1 (2013)

S. Singh, A. K. Patra, B. Barin (UG), E. del Barco and B. Ozyilmaz.
“Spin Pumping in Permalloy/Graphene and Permalloy/Graphite Interfaces”
IEEE Trans. Magn., 49, 3147 (2013).

A. K. Patra, S. Singh, B. Barin (UG), Y. Lee, J.-H. Ahn, E. del Barco, E. R. Mucciolo, and B. Ozyilmaz.
“Dynamic spin injection into chemical vapor deposited graphene”
Appl. Phys. Lett. 101, 162407 (2012).

Other publications by the group