Ferromagnetic order induced on graphene by Ni/Co proximity effects

Abstract

We build a tight-binding Hamiltonian describing Co/Ni over graphene, contemplating ATOP (a Co/Ni atom on top of each Carbon atom of one graphene sublattice) and HCP (one Co/Ni atom per Graphene plaquette) configurations. For the ATOP configuration the orbitals involved, for the Co/Ni, are the d z 2 −r 2 which most strongly couples to one graphene sublattice and the dxz, dyz orbitals that couple directly to the second sublattice site. Such configuration is diagonal in pseudospin and spin space, yielding electron doping of the graphene and antiferro-magnetic ordering in the primitive cell in agreement with DFT calculations. The second, HCP configuration is symmetric in the graphene sublattices and only involves coupling to the dxz, dyz orbitals. The register of the lattices in this case allows for a new coupling between nearest neighbour sites, generating non-diagonal terms in the pseudo-spin space and novel spin-kinetic couplings mimicking a spin-orbit coupling generated by a magnetic coupling. The resulting proximity effect in this case yields ferromagnetic order in the graphene substrate. We derive the band structure in the vicinity of the K points for both configurations, the Bloch wavefunctions and their spin polarization.

Spin-orbit Coupling Modulation in DNA by Mechanical Deformations

“…The effective overlaps are a result of the presence of the atomic spin-orbit coupling, using the Slater-Koster formulation [27,28] and a lowest-order matrix perturbation theory as proposed in ref. [29]. The effective SO coupling obtained recovers that of ref.…”

“…Here we derive the effective Hamiltonian of the DNA incorporating spin coupling from the more compact approach of band folding. [29,33] We consider an intrinsic atomic SO coupling (associated to C or N for the DNA bases) given by…”

“…The matrix elements E σ,π µµ ′ that represent the overlaps of bare orbitals are expressed as a linear combination of Slater-Koster parameters V σ,π µµ ′ which are related to the different types of molecular bonding (σ, π) between the atomic wavefunctions of the µ and µ' orbitals. [29,34] These elements obey the commutation rule V ll' = (-1) l+l' V l'l where l is the orbital angular momentum quantum number (l = 1 for p orbitals). Harrison et al [34] proposes an empirical expression for orbital overlaps as a function of the interatomic distance R jı , given that…”

Tunable induced magnetic moment and in-plane conductance of graphene in Ni/graphene/Ni nano-spin-valve-like structure: A first principles study

“…The magnetic configuration, which is initiated by the magnetic interaction of of graphene, since the previous studies have only reported that the induced magnetic moment of graphene is either in the AFM configuration [31] or FM configuration [32]. An additional remarkable point is that the total energy difference between the anti-parallel and parallel configurations is in the order of meV, which implies that the magnetic configuration change does not require an extremely high external magnetic field.…”

Proximity-induced spin-orbit effects in graphene on Au

“…Graphene/transition metal interfaces have been recognized as a very attractive hybrid systems [1][2][3][4][5] since its proximity may lend fascinating properties that the otherwise isolated graphene layer lacks. Namely, the gate controlled dopability [6], the transfer of ferro and antiferromagnetism [1,7], and the induced strong spin-orbit coupling [8], just to mention a few. In addition, more complex transition metal substrates such as transition metal dichalcogenides on few-layer graphene hybrid spin-valves have shown to induce opto-valley spin-injection due to its large SO coupling [9,10].…”