Highly efficient spin-orbit torque and switching of layered ferromagnet Fe3GeTe2

Among van der Waals (vdW) layered ferromagnets, Fe3GeTe2 (FGT) is an excellent candidate material to form FGT/heavy metal heterostructures for studying the effect of spin-orbit torques (SOT). Its metallicity, strong perpendicular magnetic anisotropy built in the single atomic layers, relatively high Curie temperature (Tc about 225 K) and electrostatic gate tunability offer a tantalizing possibility of achieving the ultimate high SOT limit in monolayer all-vdW nanodevices. The spin current generated in Pt exerts a damping-like SOT on FGT magnetization. At about 2.5x1011 A/m2 current density,SOT causes the FGT magnetization to switch, which is detected by the anomalous Hall effect of FGT. To quantify the SOT effect, we measure the second harmonic Hall responses as the applied magnetic field rotates the FGT magnetization in the plane. Our analysis shows that the SOT efficiency is comparable with that of the best heterostructures containing three-dimensional (3D) ferromagnetic metals and much larger than that of heterostructures containing 3D ferrimagnetic insulators. Such large efficiency is attributed to the atomically flat FGT/Pt interface, which demonstrates the great potential of exploiting vdW heterostructures for highly efficient spintronic nanodevices

Surfactant-assisted synthesis of nanoporous nickel sulfide flakes and their hybridization with reduced graphene oxides for supercapacitor applications

We report a simple soft-templating strategy for the synthesis of nanoporous crystalline nickel sulfide with two-dimensional (2-D) morphology. The nickel sulfide phases and morphologies are varied by changing the hydrothermal temperatures applied. Furthermore, the nanoporous nickel sulfide (PNS) flakes can be hybridized with reduced graphene oxide (rGO) sheets. As compared to bare PNS flakes, the PNS/rGO composite, containing 40% rGO, exhibits a superior electrochemical performance in terms of specific capacitance and cyclic stability. The specific capacitance of this composite is evaluated by a three-electrode system, and it shows the highest specific capacitance of 1312 F g(-1) at a scan rate of 5 mV s(-1). In addition, this composite is also assembled to form an asymmetric supercapacitor with zeolitic imidazolate framework (ZIF-8)-derived carbon as a negative electrode, which gives a highest specific capacitance of 47.85 F g(-1) at 2 A g(-1), a high energy density of 17.01 W h kg(-1), and a high power density of 10 kW kg(-1)

Controlled synthesis of highly crystallized mesoporous Mn2O3 and Mn3O4 by using anionic surfactants

Mesostructured manganese oxide (Mn3O4) is prepared by a soft-templating method employing sodium dodecyl sulfate (SDS) as a structure-directing agent. By removing the template from the as-prepared mesostructured Mn3O4 by extraction or calcination, we successfully synthesized highly crystallized mesoporous Mn3O4 or Mn2O3, respectively, with different crystalline structures

Layer-dependence study of two-dimensional ferromagnets: Fe3GeTe2 and Fe5Ge2Te2

We have investigated the electrical transport properties of nanodevices fabricated from exfoliated flakes of two-dimensional metallic ferromagnets Fe3GeTe2 (FGT) and Fe5Ge2Te2 (FG2T) down to below three layers in thickness. The per-layer anomalous Hall conductivity even in thick FGT and FG2T devices is found to be much smaller than ∼e2h, the approximate value calculated for thick undoped crystals. Moreover, we obtain a power-law scaling relation between the per-layer anomalous Hall and per-layer longitudinal conductivities with an exponent close to 1.6, which agrees with the universal value for poor ferromagnetic conductors. Both FGT and FG2T devices show clear layer-dependent Curie temperatures and layer-dependent perpendicular magnetic anisotropy, with FG2T dominating the former and FGT dominating the latter for all thicknesses. Despite their declining trend as the device thickness decreases, both Curie temperature and magnetic anisotropy retain a significant fraction of their bulk values (>60% and >80% of the bulk values, respectively, even in the thinnest FG2T device), indicating attractive potential for practical applications

Synthesis and Characterization of alpha-NiMoO4 Nanorods for Supercapacitor Application

We report the synthesis of electrode materials based on one-dimensional -NiMoO4 nanorods for application as a supercapacitor. The structure and morphology of the electrodes were characterized by powder X-ray diffraction, Raman analysis, X-ray photoelectron spectroscopy, and scanning and transmission electron microscopy. The maximum specific capacitance obtained from electrochemical measurements on a standard three-electrode system was 730 Fg(-1) at a scan rate of 5 mVs(-1). Furthermore, an asymmetric supercapacitor (ASC) was fabricated in which the NiMoO4 nanorods were used as the positive electrode and reduced graphene oxide was used as the negative electrode. The maximum specific energy obtained from the ASC study was 12.31 Whkg(-1) at a specific current of 0.5 Ag-1 in an aqueous KOH electrolyte. This ASC cell showed good stability with 85% capacitance retention up to 2000 cycles. These results reveal that our ASC shows a high performance and specific energy as well as good cycling stability

Graphene- and Phosphorene-like Boron Layers with Contrasting Activities in Highly Active Mo₂B₄ for Hydrogen Evolution

Two different boron layers, flat (graphene-like) and puckered (phosphorene-like), found in the crystal structure of Mo₂B₄ show drastically different activities for hydrogen evolution, according to Gibbs free energy calculations of H-adsorption on Mo₂B₄. The graphene-like B layer is highly active, whereas the phosphorene-like B layer performs very poorly for hydrogen evolution. A new Sn-flux synthesis permits the rapid single-phase synthesis of Mo₂B₄, and electrochemical analyses show that it is one of the best hydrogen evolution reaction active bulk materials with good long-term cycle stability under acidic conditions. Mo₂B₄ compensates its smaller density of active sites if compared with highly active bulk MoB₂ (which contains only the more active graphene-like boron layers) by a 5-times increase of its surface area