Theoretical study of spin-dependent electron transport in atomic Fe nanocontacts

Abstract

We present theoretical predictions of spintronic transport phenomena that should be observable in ferromagnetic Fe nanocontacts bridged by chains of Fe atoms. We develop appropriate model Hamiltonians based on semi-empirical considerations and the known electronic structure of bulk Fe derived from ab initio density functional calculations. Our model is shown to provide a satisfactory description of the surface properties of Fe nano-clusters as well as bulk properties. LippmannSchwinger and Green's function techniques are used together with Landauer theory to predict the current, magneto-resistance, and spin polarization of the current in Fe nanocontacts bridged by atomic chains under applied bias. Unusual device characteristics are predicted including negative magneto-resistance and spin polarization of the current, as well as spin polarization of the current for anti-parallel magnetization of the Fe nanocontacts under moderate applied bias. We explore the effects that stretching the atomic chain has on the magneto-resistance and spin polarization and predict a cross-over regime in which the spin polarization of the current for parallel magnetization of the contacts switches from negative to positive. We find resonant transmission due to dangling bond formation on tip atoms as the chain is stretched through its breaking point to play an important role in spin-dependent transport in this regime. The physical mechanisms underlying the predicted phenomena are discussed.PACS numbers: 75.47.-m,73.63.-b,72.25.-b,72.10.-d

Gate-tunable valley currents, nonlocal resistances, and valley accumulation in bilayer graphene nanostructures

“…A variety of different methods for calculating quantum transport coefficients within tight-binding formalisms have been developed and applied in the literature. They include Landauer mode counting applied to calculated quasi-one-dimensional band structures, 24,25 recursive Green's function techniques, [26][27][28][29] non-equilibrium Green's function methods, 30,31 stabilized transfer matrix methods, [32][33][34] and solution of the Lippmann-Schwinger equation, [35][36][37] among others. In the present work we chose the Lippmann-Schwinger approach for the following reasons: It is very flexible, lending itself well to calculations of transport in the linear response regime for tight-binding models of nanostructures of many different materials, with arbitrary geome- tries.…”

“…In the present work we chose the Lippmann-Schwinger approach for the following reasons: It is very flexible, lending itself well to calculations of transport in the linear response regime for tight-binding models of nanostructures of many different materials, with arbitrary geome- tries. This versatility has made possible its application to theoretical studies of electron transport in 2D semiconductor nanostructures, 35 in disordered metal nanostructures 36 , in ferromagnetic atomic contacts, 37 in monolayer graphene nanostructures, 13 in molecules bridging transition metal electrodes 38 and gold electrodes, 39 in molecular spin current rectifiers, 40 in arrays of molecules on silicon, 41 in electrochemically gated protein nanowires, 42 in single molecule nanomagnets bridging metal electrodes, 43 in Fe/GaAs spin valves, 44 in scanning tunneling microscopy of molecules, 45 in molecular electroluminescence, 46 in ballistic electron spectroscopy of buried molecules, 47 in vibrational spectroscopy of molecular junctions, 48 and others. The Lippmann-Schwinger equation is readily applicable to calculations of transport in nanostructures with arbitrary numbers of electrical contacts 13 when combined with the Büttiker-Landauer formalism 14 .…”

“…In this study, each contact is represented by a group of semi-infinite one-dimensional tight-binding leads with one orbital per site, as in many previous theoretical studies of quantum transport. [37][38][39][40][41][42][43][44][45][46][47][48] These ideal leads (represented by wavy lines in Fig. 1) are attached to edge sites of both graphene layers.…”

Stability of the V and Co atomic wires: a first-principles study

“… 36,37 In fact, in spin electronics, the thinnest magnetic chains may be used for transporting spin-polarized currents. 38 Therefore electron spin polarization may lower the total energy and improve the magnetism for specific TM chains.…”