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Register a new userOrganometallic Benzene-Vanadium Wire: One-Dimensional Half-Metallic Ferromagnet
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Using density functional theory we have performed theoretical investigations of the electronic properties of a free-standing one-dimensional organometallic vanadium-benzene wire. This system represents the limiting case of multi-decker V_n(C6H6)_{n+1} clusters which can be synthesized. We predict that the ground state of the wire is a 100% spin-polarized ferromagnet (half-metal). Its density of states is metallic at the Fermi energy for the minority electrons and shows a semiconductor gap for the majority electrons. We found that the half-metallic behavior is conserved up to 12%, longitudinal elongation of the wire. However, under further stretching, the system exhibits a transition to a high-spin ferromagnetic state that is accompanied by an abrupt jump of the magnetic moment and a gain of exchange energy.
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We study spin-scattering asymmetry at the interface of two ferromagnets (FMs) based on a half-metallic Co$_{2}$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS)/CoFe interface. First-principles ballistic transport calculations based on Landauer formula for (001)-CoFe/CFMS/CoFe indicate strong spin-dependent conductance at the CFMS/CoFe interface, suggesting large interface spin-scattering asymmetry coefficient ($gamma$). Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo spin-valve (PSV) devices involving CoFe/CFMS/Ag/CFMS/CoFe structures exhibit an enhancement in magnetoresistance output owing to the formation of the CFMS/CoFe interface at room temperature (RT). This is well reproduced qualitatively by a simulation based on a generalized two-current series-resistor model with taking the presence of $gamma$ at the CFMS/CoFe interface, half-metallicity of CFMS, and combinations of terminated atoms at the interfaces in the CPP-GMR PSV structure. We show direct evidence for large $gamma$ at a half-metallic FM/FM interface and its impact on CPP-GMR effect even at RT.
We measured the Raman spectra of ferromagnetic nearly half metal CoS2 in a broad temperature range. All five Raman active modes Ag, Eg, Tg(1), Tg(2) and Tg(3) were observed. The magnetic ordering is indicated by a change of the temperature dependences of the frequency and the line width of Ag and T g(2) modes at the Curie point. The temperature dependence of the frequencies and linewidths of the Ag, Eg, Tg(1), T g(2) modes in the paramagnetic phase can be described in the framework of the Klemens approach. Hardening of the Tg(2), Tg(1) and A g modes on cooling can be unambiguously seen in the ferromagnetic phase. The linewidths of Tg(2) and Ag modes behave a natural way at low exciting laser power (decrease with decreasing temperature) in the ferromagnetic phase. At high exciting laser power the corresponding linewidths increase at temperature decreasing below the Curie temperature. Then as can be seen the line width of Ag mode reaches a maxima at about 80K. This intriging feature probably signifies a specific channel of the optical phonon decay in the ferromagnetic phase of CoS2. Tentative explanations of some of the observed effects are given, taking into account the nearly half metallic nature of CoS2.
We consider electron transport in a nearly half-metallic ferromagnet, in which the minority spin electrons close to the band edge at the Fermi energy are Anderson-localized due to disorder. For the case of spin-flip scattering of the conduction electrons due to the absorption and emission of magnons, the Boltzmann equation is exactly soluble to the linear order. From this solution we calculate the temperature dependence of the resistivity due to single magnon processes at sufficiently low temperature, namely $k_BTll D/L^2$, where $L$ is the Anderson localization length and $D$ is the magnon stiffness. And depending on the details of the minority spin density of states at the Fermi level, we find a $T^{1.5}$ or $T^{2}$ scaling behavior for resistivity. Relevance to the doped perovskite manganite systems is discussed.
Nano-thick metallic transition metal dichalcogenides such as VS$_{2}$ are essential building blocks for constructing next-generation electronic and energy-storage applications, as well as for exploring unique physical issues associated with the dimensionality effect. However, such 2D layered materials have yet to be achieved through either mechanical exfoliation or bottom-up synthesis. Herein, we report a facile chemical vapor deposition route for direct production of crystalline VS$_{2}$ nanosheets with sub-10 nm thicknesses and domain sizes of tens of micrometers. The obtained nanosheets feature spontaneous superlattice periodicities and excellent electrical conductivities (~3$times$10$^{3}$ S cm$^{-1}$), which has enabled a variety of applications such as contact electrodes for monolayer MoS$_{2}$ with contact resistances of ~1/4 to that of Ni/Au metals, and as supercapacitor electrodes in aqueous electrolytes showing specific capacitances as high as 8.6$times$10$^{2}$ F g$^{-1}$. This work provides fresh insights into the delicate structure-property relationship and the broad application prospects of such metallic 2D materials.
By means of first-principles density functional theory calculations, we find that hydrogen-passivated ultrathin silicon nanowires (SiNWs) along [100] direction with symmetrical multiple surface dangling bonds (SDBs) and boron doping can have a half-metallic ground state with 100% spin polarization, where the half-metallicity is shown quite robust against external electric fields. Under the circumstances with various SDBs, the H-passivated SiNWs can also be ferromagnetic or antiferromagnetic semiconductors. The present study not only offers a possible route to engineer half-metallic SiNWs without containing magnetic atoms but also sheds light on manipulating spin-dependent properties of nanowires through surface passivation.
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