The impact of Fe atom on the spin-filter and spin thermoelectric properties of Au-Fe@C20-Au monomer and dimer systems

Based on density functional theory and non-equilibrium Green's function formalism, we explore the effect of Fe atom in Au-Fe@C20-Au monomer and dimer systems in comparison with the C20 fullerene molecular junctions. We calculate the spin-dependent transmission coefficient, spin polarization and also their spin thermoelectric coefficients to investigate magnetic properties in the system. Our results indicate that the presence of Fe atoms enhances substantially the spin-filter and increases the spin figure of merit in the dimer system. We suggest that the Au-(Fe@C20)2-Au system is a suitable junction for designing spin-filtering and spin thermoelectric devices and eventually it is a good candidate for spintronic applications.

Enhanced robustness of half-metallicity in VBr3 nanowires by strains and transition metal doping

The study of half-metallic behavior for transition metal tribromide nanowires is of great significance to the basic research and application in spintronics. We have theoretically investigated the spin transport properties of half-metallic VBr3 nanowires sandwiched between Au(100) electrodes. For the VBr3 nanowire with a length of 24.75 Å, the spin-filter efficiency (SFE) achieves 100% when the applied bias is less than 0.4 V. The robustness of half-metallic behavior in VBr3 nanowires is investigated by strains and transition metal doping. The bias range of VBr3 nanowires exhibiting perfect SFE is extended by tensile strains, while it becomes narrower under compressive strains. For VBr3 nanowires doped with Co and Cr, the bias range with ideal SFE is significantly broadened at a low doping concentration. In particular, the VBr3 nanowire doped with 1 Cr atom exhibits perfect SFE in an extremely wide bias range of 0-1.0 V. Our results show that the robustness of half-metallicity of VBr3 nanowires can be improved by tensile strains or certain doping, which provides promising ways for further design of high-performance spintronic devices.

Half-metallic behavior in ruthenium-cyclopentadienyl organometallic sandwich molecules

We have theoretically investigated spin transport properties of one-dimensional ruthenium-cyclopentadienyl sandwich molecules, Ru_n(Cp)_n+1, between two gold electrodes. Calculations were performed based on the non-equilibrium Green's function formalism and density functional theory. The results clearly reveal that for n = 1, no spin-polarized behavior is observed due to the fully occupied valence shell of ruthenocene molecule, while for the higher n values, the total magnetic moments increase with increasing size of the cluster and a half metallic behavior has been achieved. This can be attributed to the altered ligand field of π-conjugate systems generated by metal centers. Interestingly, for n values higher than 1, not only do the current-voltage curves exhibit an efficient spin-current generation but also a pronounced negative differential resistance behavior can be detected in the bias region. Our results will be strongly informative for the design and control of high-performance organometallic sandwich molecules based on spin-electronic devices.

Magneto-Seebeck effect in Co2FeAl/MgO/Co2FeAl: first-principles calculations

The magneto-Seebeck effect has recently attracted considerable attention because of its novel fundamental physics and future potential application in spintronics. Herein, employing first-principles calculations and the spin-resolved Boltzmann transport theory, we have systematically investigated the electronic structures and spin-related transport properties of Co2FeAl/MgO/Co2FeAl multilayers with parallel (P) and anti-parallel (AP) magnetic alignment. Our results indicate that the sign of tunneling magneto-Seebeck (TMS) value with Co2/O termination is consistent with that of the measured experimental result although its value (-221%) at room temperature is smaller than the experimental one (-95%). The calculated spin-Seebeck coefficients of the Co2/O termination with P and AP states and the FeAl/O termination with the AP state are all larger than other typical Co2MnSi/MgO/Co2MnSi heterostructures. By analyzing the geometries, electronic structures, and magnetic behaviors of two different terminations (Co2/O and FeAl/O terminations), we find that the two terminations in the interface region form anti-bonding and bonding states, reconstructing the energy gap, changing the magnetic moment of O atoms, and improving the spin-polarization (-82%). This phenomenon can be ascribed to the charge transfer and hybridization between Co/Fe 3d and O 2p states, which also results in a bowknot orbital shape of Co atoms with Co2/O termination and an ankle shape of Co atoms with FeAl/O termination far away from the interface. Moreover, there are spin-splitting transmission gaps with the Co2/O-termination around the Fermi level, while the transmission gaps with the FeAl/O-termination are closed and thus show a typical metallic character. Our findings will guide the experimental design of magneto-Seebeck devices for future spintronic applications.

Zigzag C2N nanoribbons with edge modifications as multi-functional spin devices

Recently, a holey two-dimensional (2D) C₂N crystal with a wide band gap has been successfully synthesized. However, its non-magnetic property largely limits real applications in spintronics. Here we find that edge magnetism can be introduced by tailoring the holey 2D C₂N crystal into nanoribbons with zigzag edges. When edge N atoms are bare or passivated by H atoms, the device can be used to design high-performance thermospin devices and thermal rectifiers. This is ascribed to the emergence of a spin semiconducting property with a wide band gap. Moreover, if the edge N atoms are passivated by O atoms, the device shows a half-metallic property; meanwhile an obvious spin Seebeck effect can also be observed when a temperature difference is applied across the device.

Chemical substitution assisted ion sensing with organic molecules: a case study of naphthalene

Using first-principles calculations, we predict that a naphthalene molecule with N substitutions for the –CH groups is a good system for H⁺ sensing.

Giant spin thermoelectric effects in all-carbon nanojunctions

We investigate the thermospin properties of an all-carbon nanojunction constructed by a graphene nanoflake (GNF) and zigzag-edged graphene nanoribbons (ZGNRs), bridged by the carbon atomic chains.

Spin caloritronics of blue phosphorene nanoribbons

We report a first-principles study of the magnetic properties and spin caloritronics of zigzag-type blue phosphorene nanoribbons (zBPNRs).

Improvement of thermoelectric efficiency of the polyaniline molecular junction by the doping process

Thermoelectric properties of a polyaniline molecular junction with face centered cubic electrodes are investigated using the Green function formalism in a linear response regime in the presence of the doping process.

Improving the bias range for spin-filtering by selecting proper electrode materials

Using the non-equilibrium Green’s function method combined with density function theory, we investigate the spin transport for carbon chains connected to electrodes of different materials.

Temperature-controlled giant thermal magnetoresistance behaviors in doped zigzag-edged silicene nanoribbons

Based on the nonequilibrium Green's function (NEGF) method combined with density functional theory (DFT), we investigate the spin-dependent thermoelectric transport properties of zigzag-edged silicene nanoribbons (ZSiNRs) doped by an Al–P bonded pair at different edge positions.