The origin of half-metallicity in conjugated electron systems--a study on transition-metal-doped graphyne

Emergence of magnetic anisotropy by surface adsorption of transition metal dimers on γ-graphyne framework

In this paper a systematic study is carried out to demonstrate the structural stability and magnetic novelty of adsorbing transition metal (TM) dimers (A-B) on graphyne (GY) surface, GY@A-B. Our research points out that the dimers are strongly adsorbed onto GY due to their large natural pores and the electron affinity of the sp-hybridized carbon atoms. Electronic properties of these dimer-graphyne composite systems are of particular importance as they behave as degenerate semiconductors with partial occupation of states atE_F. Furthermore, their remarkable spin polarization (>80%) at Fermi energy (E_F) can be of paramount importance in spintronics applications. Most of the GY@A-B structures exhibit large magnetic anisotropies as well as magnetic moments along the out-of-plane direction with respect to the GY surface. Particularly, GY@Co-Ir, GY@Ir-Ir and GY@Ir-Os structures possess positive magnetic anisotropic energies (MAE) of 121 meV, 81 meV and 137 meV, respectively, which are comparable to other well-known TM dimer doped systems. The emergence of high MAE can be understood using the second-order perturbation theory on the basis of the strong spin-orbit coupling (SOC) between the two TMs and the degeneracy of their d-orbitals nearE_F. A close correspondence between the simulated and the analytical results has been established through our work. Further, a simple estimation shows that, GY@A-B structures have the potential to store data up to 64 PB m^-2. These intriguing electronic characteristics along with magnetism suggest GY@A-B to be a promising material for future magnetic storage devices.

A high performance N-doped graphene nanoribbon based spintronic device applicable with a wide range of adatoms

Designing and fabricating nanosize spintronic devices is a crucial task to develop information technology of the future. However, most of the introduced spin filters suffer from several limitations including difficulty in manipulating the spin current, incapability in utilizing a wide range of dopants to provide magnetism, or obstacles in their experimental realization. Here, by employing first principles calculations, we introduce a structurally simple and functionally efficient spin filter device composed of a zigzag graphene nanoribbon (ZGNR) with an embedded nitrogenated divacancy. We show that the proposed system, possessing a robust ferromagnetic (FM) ordering, exhibits perfect half metallic behavior in the absence of frequently used transition metals (TMs). Our calculations also show that the suggested system is compatible with a wide range of adatoms including basic metals, metalloids, and TMs. It means that besides d electron magnetism originating from TMs, p electrons of incorporated elements of the main group can also cause half metallicity in the electronic structure of the introduced system. Our system exploiting the robustness of doping-induced FM ordering would be beneficial for promising multifunctional spin filter devices.

Ferromagnetism and Half-Metallicity in a High-Band-Gap Hexagonal Boron Nitride System

Metal-free half-metallicity is the subject of intense research in the field of spintronics devices. Using density functional theoretical calculations, atom-thin hexagonal boron nitride (h-BN)-based systems are studied for possible spintronics applications. Ferromagnetism is observed in patterned C-doped h-BN systems. Interestingly, such a patterned C-doped h-BN exhibits half-metallicity with a Curie temperature of approximately 324 K at a particular C-doping concentration. It shows half-metallicity more than metal-free systems studied to date. Thus, such a BN-based system can be used to achieve a 100 % spin-polarised current at the Fermi level. Furthermore, this C-doped system shows excellent dynamical, thermal, and mechanical properties. Therefore, a stable metal-free planar ferromagnetic half-metallic h-BN-based system is proposed for use in room-temperature spintronics devices.