Spin Filtering through Single‐Wall Carbon Nanotubes Functionalized with Single‐Stranded DNA

High spin polarization materials or spin filters are key components in spintronics, a niche subfield of electronics where carrier spins play a functional role. Carrier transmission through these materials is “spin selective,” that is, these materials are able to discriminate between “up” and “down” spins. Common spin filters include transition metal ferromagnets and their alloys, with typical spin selectivity (or, polarization) of ≈50% or less. Here carrier transport is considered in an archetypical one‐dimensional molecular hybrid in which a single wall carbon nanotube (SWCNT) is wrapped around by single stranded deoxyribonucleic acid (ssDNA). By magnetoresistance measurements it is shown that this system can act as a spin filter with maximum spin polarization approaching ≈74% at low temperatures, significantly larger than transition metals under comparable conditions. Inversion asymmetric helicoidal potential of the charged ssDNA backbone induces a Rashba spin‐orbit interaction in the SWCNT channel and polarizes carrier spins. The results are consistent with recent theoretical work that predicted spin dependent conductance in ssDNA‐SWCNT hybrid. Ability to generate highly spin polarized carriers using molecular functionalization can lead to magnet‐less and contact‐less spintronic devices in the future. This can eliminate the conductivity mismatch problem and open new directions for research in organic spintronics.     

Toward the Optimized Spintronic Response of Sn‐Doped IrO2 Thin Films

Amorphous and polycrystalline Sn‐doped IrO₂ thin films, Ir_1‐xSn_xO₂, are grown for the first time. Their electrical response and strength of the spin–orbit coupling are studied in order to better understand and tailor its performance as spin current detector material. These experiments prove that the resistivity of IrO₂ can be tuned over several orders of magnitude by controlling the doping content in both the amorphous and the polycrystalline state. In addition, growing amorphous samples increase the resistivity, thus improving the spin current to charge current conversion. As far as the spin–orbit coupling is concerned, the system not only remains in a strong spin–orbit coupling regime but it seems to undergo a slight enhancement in the amorphous state as well as in the Sn‐doped samples.     

Ultrafast Orbital‐Oriented Control of Magnetization in Half‐Metallic La0.7Sr0.3MnO3 Films

Manipulating spins by ultrafast pulse laser provides a new avenue to switch the magnetization for spintronic applications. While the spin–orbit coupling is known to play a pivotal role in the ultrafast laser‐induced demagnetization, the effect of the anisotropic spin–orbit coupling on the transient magnetization remains an open issue. This study uncovers the role of anisotropic spin–orbit coupling in the spin dynamics in a half‐metallic La_0.7Sr_0.3MnO₃ film by ultrafast pump–probe technique. The magnetic order is found to be transiently enhanced or attenuated within the initial sub‐picosecond when the probe light is tuned to be s‐ or p‐polarized, respectively. The subsequent slow demagnetization amplitude follows the fourfold symmetry of the ${\mathrm{d}}_{x^2?y^2}$ orbitals as a function of the polarization angles of the probe light. A model based on the Elliott–Yafet spin‐flip scatterings is proposed to reveal that the transient magnetization enhancement is related to the spin‐mixed states arising from the anisotropic spin–orbit coupling. The findings provide new insights into the spin dynamics in magnetic systems with anisotropic spin–orbit coupling as well as perspectives for the ultrafast control of information process in spintronic devices.     

Rashba效应下三角量子阱中弱耦合束缚极化子的性质

利用线性组合算符和幺正变换相结合的方法,推导出三角量子阱中弱耦合束缚极化子的基态能量。并讨论了耦合常数,库仑束缚势和电子面密度对极化子基态能量的影响。通过对GaAs材料的数值计算,最后结果显示：由于电-声子耦合作用和Rashba效应的存在,弱耦合束缚极化子的基态能量由四部分组成,而且弱耦合束缚极化子的基态能量随耦合常数,库仑束缚势和电子面密度都发生了分裂。     

Grafting Single Molecule Magnets on Gold Nanoparticles

The chemical synthesis and characterization of the first hybrid material composed by gold nanoparticles and single molecule magnets (SMMs) are described. Gold nanoparticles are functionalized via ligand exchange using a tetrairon(III) SMM containing two 1,2‐dithiolane end groups. The grafting is evidenced by the shift of the plasmon resonance peak recorded with a UV–vis spectrometer, by the suppression of nuclear magnetic resonance signals, by X‐ray photoemission spectroscopy peaks, and by transmission electron microscopy images. The latter evidence the formation of aggregates of nanoparticles as a consequence of the cross‐linking ability of Fe₄ through the two 1,2‐dithiolane rings located on opposite sides of the metal core. The presence of intact Fe₄ molecules is directly proven by synchrotron‐based X‐ray absorption spectroscopy and X‐ray magnetic circular dichroism spectroscopy, while a detailed magnetic characterization, obtained using electron paramagnetic resonance and alternating‐current susceptibility, confirms the persistence of SMM behavior in this new hybrid nanostructure.     

Electrical Detection of Spin Precession in Freely Suspended Graphene Spin Valves on Cross‐Linked Poly(methyl methacrylate)

Spin injection and detection is achieved in freely suspended graphene using cobalt electrodes and a nonlocal spin‐valve geometry. The devices are fabricated with a single electron‐beam‐resist poly(methyl methacrylate) process that minimizes both the fabrication steps and the number of (aggressive) chemicals used, greatly reducing contamination and increasing the yield of high‐quality, mechanically stable devices. As‐grown devices can present mobilities exceeding 10⁴ cm² V^?1 s^?1 at room temperature and, because the contacts deposited on graphene are only exposed to acetone and isopropanol, the method is compatible with almost any contacting material. Spin accumulation and spin precession are studied in these nonlocal spin valves. Fitting of Hanle spin precession data in bilayer and multilayer graphene yields a spin relaxation time of ～125‐250 ps and a spin diffusion length of 1.7‐1.9 μm at room temperature.