Spin-Polarized Current in Ferromagnetic Half-Metallic Transition-Metal Iodide Nanowires (original) (raw)
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Spintronic devices are of fundamental interest for their nonvolatility and great potential for low-power electronics applications. The implementation of those devices usually favors materials with long spin lifetime and spin diffusion length. Recent spin transport studies on semiconductor nanowires have shown much longer spin lifetimes and spin diffusion lengths than those reported in bulk/thin films. In this paper, we have reviewed recent progress in the electrical spin injection and transport in semiconductor nanowires and drawn a comparison with that in bulk/thin films. In particular, the challenges and methods of making high-quality ferromagnetic tunneling and Schottky contacts on semiconductor nanowires as well as thin films are discussed. Besides, commonly used methods for characterizing spin transport have been introduced, and their applicability in nanowire devices are discussed. Moreover, the effect of spin-orbit interaction strength and dimensionality on the spin relaxation and hence the spin lifetime are investigated.
2003 Third IEEE Conference on Nanotechnology, 2003. IEEE-NANO 2003., 2003
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Physical Review B, 2007
The magnetic and electronic properties of both linear and zigzag atomic chains of all 3d transition metals have been calculated within density functional theory with the generalized gradient approximation. The underlying atomic structures were determined theoretically. It is found that all the zigzag chains except the nonmagnetic (NM) Ni and antiferromagnetic (AF) Fe chains which form a twisted two-legger ladder, look like a corner-sharing triangle ribbon, and have a lower total energy than the corresponding linear chains. All the 3d transition metals in both linear and zigzag structures have a stable or metastable ferromagnetic (FM) state. Furthermore, in the V, Cr, Mn, Fe, Co linear chains and Cr, Mn, Fe, Co, Ni zigzag chains, a stable or metastable AF state also exists. In the Sc, Ti, Fe, Co, Ni linear structures, the FM state is the ground state whilst in the V, Cr and Mn linear chains, the AF state is the ground state. The electronic spin-polarization at the Fermi level in the FM Sc, V, Mn, Fe, Co and Ni linear chains is close to 90% or above, suggesting that these nanostructures may have applications in spin-transport devices. Interestingly, the V, Cr, Mn, and Fe linear chains show a giant magneto-lattice expansion of up to 54 %. In the zigzag structure, the AF state is more stable than the FM state only in the Cr chain. Both the electronic magnetocrystalline anisotropy and magnetic dipolar (shape) anisotropy energies are calculated. It is found that the shape anisotropy energy may be comparable to the electronic one and always prefers the axial magnetization in both the linear and zigzag structures. In the zigzag chains, there is also a pronounced shape anisotropy in the plane perpendicular to the chain axis. Nonetheless, in the FM Ti, Mn, Co and AF Cr, Mn, Fe linear chains, the electronic anisotropy is perpendicular, and it is so large in the FM Ti and Co as well as AF Cr, Mn and Fe linear chains that the easy magnetization axis is perpendicular. In the AF Cr and FM Ni zigzag structures, the easy magnetization direction is also perpendicular to the chain axis but in the ribbon plane. Remarkably, the axial magnetic anisotropy in the FM Ni linear chain is gigantic, being ∼ 12 meV/atom, suggesting that Ni nanowires may have applications in ultrahigh density magnetic memories and hard disks. Interestingly, there is a spin-reorientation transition in the FM Fe and Co linear chains when the chains are compressed or elongated. Large orbital magnetic moment is found in the FM Fe, Co and Ni linear chains. Finally, the band structure and density of states of the nanowires have also been calculated to identify the electronic origin of the magnetocrystalline anisotropy and orbital magnetic moment.
Magnetism of Transition Metal Nanowires
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In this thesis we investigated structural, electronic and magnetic properties of 3d (light) transition metal (TM) atomic chains and Cr nanowires using firstprinciples pseudopotential plane wave calculations. Infinite periodic linear, dimerized linear and planar zigzag chain structures, as well as their short segments consisting of finite number of atoms and chromium nanowires have been considered. For most of the infinite periodic chains, neither linear nor dimerized linear structures are favored; to lower their energy the chains undergo a structural transformation to form planar zigzag and dimerized zigzag geometries. Dimerization in both infinite and finite chains are much stronger than the usual Peierls distortion and appear to depend on the number of 3d-electrons. As a result of dimerization, a significant energy lowering occurs which, in turn, influences the stability and physical properties. Metallic linear chain of vanadium becomes half-metallic upon dimerization. Infinite linear chain of scandium also becomes half-metallic upon transformation to the zigzag structure. The end effects influence the geometry, energetics and the magnetic ground state of the finite chains. Structure optimization performed using noncollinear approximation indicates significant differences from the collinear approximation. Variation of the cohesive energy of infinite and finite-size chains with respect to the number of 3d-electrons are found to mimic the bulk behavior pointed out by Friedel. Furthermore, we considered Cr nanowires, which have cross section comprising a few (4,5-9,12) atoms. Chromium nanowires are found to be in a local minimum in the Born-Oppenheimer surface and are ferrimagnetic metals. The type of coupling, as for ferromagnetic or antiferromagnetic, between neighboring Cr atoms depends on their interatomic distances. The spin-orbit coupling of finite chains are found to be negligibly small for finite molecules and Cr nanowires.
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Physical Review B, 2002
We present ab initio calculations for metallic nanowires with a diameter of few atoms. The electronic structure is calculated using the screened Korringa Kohn Rostoker Green's function method, while electronic transport properties are obtained using a Green's function formulation of the Landauer formalism. We focus on the effect of scattering due to transition metal impurities on the conductance of a Cu wire. For a single defect, our results show a reduction of the transmission for energies at the impurity d state and due to the spinpolarization conductance is different for the two-spin directions causing a spin-filter effect. For a defect pair, quantum interference effects lead to a complicated energy dependence of the conductance.
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We compare the spin-orbit interaction (SOI) in InAs nanowires grown in the conventional 0001 crystal direction and the perpendicular 0110 direction. It is theoretically shown that, for individual transverse modes, the intrinsic contribution due to the bulk inversion asymmetry of the crystal vanishes for wires in the 0001 direction but remains finite for 0110. Experimental spin-orbit scattering lengths extracted from low-temperature magnetoresistance measurements of individual nanowires yields, however, comparable values in the two cases, suggesting that the intrinsic intramode spin-orbit term is not the dominant source of the SOI. We discuss the implications for the manipulation of SOI in nanowire devices.