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PACS 72.25.Mk -Spin transport through interfaces PACS 72.10.-d -Theory of electronic transport; scattering mechanisms PACS 85.75.-d -Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fieldsAbstract -Recent experimental and theoretical studies focus on spin-mediated heat currents at interfaces between normal metals and magnetic insulators. We resolve conflicting estimates for the order of magnitude of the spin transfer torque by first-principles calculations. The spin mixing conductance G ↑↓ of the interface between silver and the insulating ferrimagnet Yttrium Iron Garnet (YIG) is dominated by its real part and of the order of 10 14 Ω −1 m −2 , i.e. close to the value for intermetallic interface, which can be explained by a local spin model.

We demonstrate a simple, efficient, yet versatile method for the realization of core-shell assembly of graphene around various metal oxide (MO) nanostructures, including nanowires (NWs) and nanoparticles (NPs). The process is driven by (i) the ring-opening reaction between the epoxy groups and amine groups in graphene oxide (GO) platelets and amine-modified MO nanostructures, respectively, and (ii) electrostatic interaction between these two components. Nearly every single NW or NP is observed to be wrapped by graphene. To the best of our knowledge, this is the first report that substrate-supported MO NWs are fully coated with a graphene shell. As an example of the functional properties of these compound materials, the graphene@a-Fe 2 O 3 core-shell NPs are investigated as the lithium-ion battery (LIB) electrode, which show a high reversible capacity, improved cycling stability, and excellent rate capability with respect to the pristine a-Fe 2 O 3 . The superior performance of the composite electrode is presumably attributed to the effectiveness of the graphene shell in preventing the aggregation, buffering the volume change, maintaining the integrity of NPs, as well as improving the conductivity of the electrode.

Charge density is one of the most important parameters of triboelectric nanogenerators since it directly determines performance; unfortunately, it is largely restricted by the phenomenon of air breakdown. Here, we design a self-improving triboelectric nanogenerator with improved charge density. A maximum effective charge density of 490 μC m−2 is obtained, which is about two times higher than the highest reported charge density of a triboelectric nanogenerator that operates in an air environment. At the beginning of the working process, the charge accumulation speed is increased 5.8 times in comparison with a triboelectric nanogenerator that is incorporated into the self-improving device. The self-improving triboelectric nanogenerator overcomes the restriction of air breakdown and exhibits an increased effective charge density, which contributes to the improvement of the output performance, and the increase of charge accumulation speed will accelerate the increase of the output power at the start of operation.

A new type of scrolled structure of Co(3)O(4)/reduced graphene oxide (r-GO) is facilely prepared through a two-step surfactant-assisted method. This assembly enables almost every single Co(3)O(4) scroll to connect with the r-GO platelets, thus leading to remarkable electrochemical performances in terms of high specific capacitance and good rate capability.

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We compute thermal spin transfer torques (TST) in Fe-MgO-Fe tunnel junctions using a first principles wave function-matching method. At room temperature, the TST in a junction with 3 MgO monolayers amounts to 10 −7 J/m 2 / K, which is estimated to cause magnetization reversal for temperature differences over the barrier of the order of 10 K. The large TST can be explained by multiple scattering between interface states through ultrathin barriers. The angular dependence of the TST can be very skewed, possibly leading to thermally induced high-frequency generation. [6] predicted that a temperature gradient induces a spin transfer torque that can excite a magnetization. Experimental evidence for the thermal spin-transfer torque has been obtained for Co-Cu-Co nanowires [7]. Slonczewski recently argued that thermal torques can be generated efficiently in spin valves with polarizing magnetic insulators [8].Magnetic tunnel junctions (MTJs) of transition metals with MgO barriers [9,10] have great potential for applications in magnetic random access memory (MRAM) elements and high-frequency generators [11][12][13][14]. An important goal of academic and corporate research remains the reduction of the critical currents necessary to induce magnetization precession and reversal [15,16] Here we predict very large thermal spin transfer torques in MTJs with thin MgO barriers, which might open new possibilities to design memory elements and high-frequency generators driven by heat currents only. We have been motivated by the strong energy dependence of electron transmission through MTJs with thin barriers due to the existence of interface resonant states [20], which should cause large thermoelectric effects. Focussing on epitaxial Fe-MgO-Fe MTJs under a temperature bias, we demonstrate the effectiveness of thermal spin transfer torques by ab initio calculations based on the Landauer-Büttiker transport formalism. Consider an (1) Here the energy-dependent spin transmission coefficient matrix from the left (right) direction is defined as twith spin current operator Ĵ n+1,n (k ) = − Re L,L ′ σ,Ĥ nL,n+1L ′ (k ) ,Ĥ nL,n+1L ′ (k ) denotes the Hamiltonian matrix in spin space [22], where

An efficient method for the preparation of benzoxazole and benzimidazole covalently grafted graphene and their application as high performance electrode materials for supercapacitors is reported. The synthesis of such covalently functionalized graphene materials first involves a cyclization reaction of carboxylic groups on graphene oxide with the hydroxyl and aminos groups on o-aminophenol and o-phenylenediamine, and subsequent reduction by hydrazine. Results of Fourier transformed infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) have confirmed that the covalent functionalization of graphene is achieved through the formation of benzoxazole and benzimidazole on the graphene sheets. The functionalized graphene materials are revealed to consist of corrugation and scrolling morphologies with less aggregation, indicating the effectiveness of functionalization in preventing restacking/aggregation of the graphene sheets. Furthermore, when applied as supercapacitor electrodes, the functionalized graphene materials exhibit good electrochemical performances in terms of high specific capacitance (730 and 781 F g À1 for benzoxazole and benzimidazole grafted graphene, respectively, at a current density of 0.1 A g À1 ) and good cycling stability, implying their potential for energy storage applications.