Single-band tight-binding parameters for Fe-MgO-Fe magnetic heterostructures (original) (raw)
Related papers
2008
Motivated by observation of very high tunnel magnetoresistance (TMR) in Fe-MgO-Fe magnetic tunnel junction devices, we propose a theoretical model for these devices based on a single-band tight-binding approximation. An effort is made to capture the band dispersions over the two dimensional transverse Brillouin zone. In the transport direction, spin dependent Hamiltonian is prescribed for Delta_1 and Delta_5 bands. Non-equilibrium Green's function formalism is then used to calculate transport. Features like voltage dependence of TMR are captured quantitatively within this simple model and the trends match well with the ones predicted by ab-initio methods and experiments.
A generic single-band tight-binding model for spin polarized transport
2008
A simple model that captures the band structure effects in quantum transport is desirable for rapid device prototyping. The motivation behind this work is to present such a model for spin polarized transport that incorporates the band structure effects and is computationally efficient. We apply this model to study transmission through bcc Fe(100) as a test case. At (ky,kz) = (0,0) in [100] direction, band dispersions match well with either an effective mass parabolic fit or a cosine fit. However, over the two dimensional transverse Brillouin zone, the band dispersions no more remain parabolic or cosine. In an effort to capture these features, band parameters are proposed using a single-band tight-binding model. Equilibrium transmission is then calculated using non-equilibrium Green's function formalism, which matches well with the one obtained using a semi-empirical extended Huckel theory. This approach is quiet general and should be able to reproduce transport properties of a wide range of magnetic and non-magnetic materials.
Spin-dependent tunneling characteristics in Fe/MgO/Fe trilayers: First-principles calculations
Solid State Communications, 2010
Spin-dependent transport properties are investigated in a single-crystal magnetic tunnel junction (MTJ) which consists of two Fe electrodes separated by an MgO insulating barrier. Our calculations are based on the first-principle density functional theory including the metal-oxide interface. Modifications are observed in the electronic and magnetic structure of the interface as a result of oxidation. Spin polarizations (SPs) more than 80% and −86% are obtained at zero temperature for clean interfaces in the parallel and anti-parallel alignments of the ferromagnetic electrodes, respectively, when a 7 monolayer MgO is used as the barrier. In the parallel alignment, the zero-bias SP is observed to be positive throughout the barrier reaching to a maximum at the central point. On the other hand, in the anti-parallel alignment, the SP of the electrodes is seen to penetrate deep into the barrier. The effects of interface oxidation on the band structure of the electrode surfaces are simulated using the fixed-spin-moment calculations. Also, we study dependence of the tunneling magnetoresistance on the barrier thickness and applied voltage in the trilayer within the effective mass approximation. It is shown that the TMR ratio decreases rapidly with increasing the barrier thickness and applied voltage. Our calculations explain qualitatively the main features of the recent experimental observations. Our results may be useful for the development of spintronic devices.
Tight binding calculation of tunneling conductance of a metal/ferromagnetic junction
Physica B: Condensed Matter, 2017
A tight binding approximation was used to describe the electronic properties of a metal/ ferromagnetic junction in a one-dimensional system. The appropriate boundary conditions were calculated to describe the quality of the interface, the non-spin-flip and spin-flip scattering potential. The BTK model was used to compute the reflection and transmission probabilities, and the Landauer formulation was used to calculate the conductance spectrum. It was found that the conductance spectrum changes slope at the bias voltage that reached the bottom of the minority band and the top of the majority band of the ferromagnetic. The conductance spectrum was suppressed for all energies when either the non-spin-flip or spin-flip scattering at the interface increased. However, the conductance spectrum can be enhanced when the interface was taken into account for the appropriate value of the spin-flip and non-spin-flip scattering. In addition, the conductance can be increased by increasing the next-nearest neighbor hopping energy in the ferromagnetic material.
Physical Review B, 2008
The effect of electronic correlations on the spin-dependent ballistic transport in Fe/MgO/Fe magnetic tunnel junctions with FeO interface layers is investigated by means of first-principles calculations. The self-interaction correction to the local spin-density approximation ͑LSDA͒ is applied to electronic states localized at the FeO layers. With respect to LSDA, the electronic and magnetic properties are significantly changed; e.g. the magnetic moment at the Fe interface is increased by 23%, the conductance is in general decreased, and the tunnel magnetoresistance ratio is reduced by up to 40%. The self-interaction correction is deemed beneficial in transport calculations for systems with localized states, e.g., those with oxide layers.
The two-bands model of the magnetic tunnel junctions in the Fe/Cr/MgO/Fe structure
2009
In this paper we present theoretical studies of spin dependent transport in Fe/Cr/MgO/Fe tunnel junctions with non-collinear alignment of magnetizations of metallic layers comprising these MTJs. Calculations are performed with use of non-equilibrium Green function technique in the framework of Keldysh formalism. WKB approximation is used for wave and Green functions in the trapezoidal barrier region under applied voltage. Electronic
First Principles Modeling of Tunnel Magnetoresistance of Fe/MgO/Fe Trilayers
Physical Review Letters, 2006
We report ab initio calculations of nonequilibrium quantum transport properties of Fe=MgO=Fe trilayer structures. The zero bias tunnel magnetoresistance is found to be several thousand percent, and it is reduced to about 1000% when the Fe=MgO interface is oxidized. The tunnel magnetoresistance for devices without oxidization reduces monotonically to zero with a voltage scale of about 0.5-1 V, consistent with experimental observations. We present an understanding of the nonequilibrium transport by investigating microscopic details of the scattering states and the Bloch bands of the Fe leads.