Single-crystal magnetotunnel junctions

Wulfhekel, Wulf; Klaúa, M.; Ullmann, Dirk; Zavaliche, F.; Kirschner, J.; Urban, R.; Monchesky, T. L.; Heinrich, B.

doi:10.1063/1.1342778

Cited by 122 publications

(89 citation statements)

References 16 publications

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“…At about 1.5V , the device "turns on" and current increases rapidly afterward. Such a turnon voltage is consistent with experimental data [4,17]. The spin-currents are shown as the dashed and dotted lines for the up-and down-channels (majority-, minoritychannel).…”

supporting

confidence: 77%

First Principles Modeling of Tunnel Magnetoresistance ofFe/MgO/FeTrilayers

et al. 2006

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By carrying out density functional theory analysis within the Keldysh non-equilibrium Green's functional formalism, we have calculated the nonlinear and non-equilibrium quantum transport properties of Fe/MgO/Fe trilayer structures as a function of external bias voltage. For well relaxed atomic structures of the trilayer, the equilibrium tunnel magnetoresistance ratio (TMR) is found to be very large and also fairly stable against small variations in the atomic structure. As a function of external bias voltage, the TMR reduces monotonically to zero with a voltage scale of about 1V, in agreement with experimental observations. We present understanding of the nonequilibrium transport properties by investigating microscopic details of the scattering states and the Bloch bands of the Fe leads.PACS numbers: 85.35.-p, 72.25.-b, 85.65.+h Since the prediction and elegant physics explanation [1,2] that magnetic tunnel junction (MTJ) of Fe/MgO/Fe trilayer structure may have very high tunnel magnetoresistance (TMR), MgO based MTJ has progressed at a rapid pace in recent years and produced the highest measured TMR at room temperature: several groups [3,4] reported TMR ratio in the range of 180% to 250%. TMR effect presents an excellent opportunity for spintronics, it is the key to magnetoresistive random-access-memory . There are, however, a number of important issues remain to be understood from atomic first principles. Most existing work predicted[1, 2] TMR to be greater than 1000%, experimental data are still lower. More seriously is that experimental data on MgO based MTJs show a monotonically decreasing TMR as a function of applied bias voltage [3,4] and it reduces to zero when bias is about one volt. To the best of our knowledge, there have been two atomistic calculations of bias dependence of TMR for MgO barriers [7,8], both used the Korringa-Kohn-Rostoker numerical technique. Ref.7 predicted a substantial increase of TMR versus bias for the asymmetric system analyzed there, while Ref.8 found a roughly constant TMR, a decaying TMR, or an entirely negative TMR versus bias depending on atomic structures of the interface. The origin of these differences were not clear. Earlier theory[9] on Al 2 O 3 based MTJs has attributed small bias dependence of magneto-resistance to magnon scattering. Given the extreme importance of MgO based MTJ in near future spintronics and the accumulated experimental data, further quantitative understanding on quantum transport in Fe/MgO/Fe at finite bias is urgently needed.Here we present a first principles atomistic analysis of nonlinear and non-equilibrium quantum transport in Fe/MgO/Fe MTJ. We use a state-of-the-art quantum transport technique [10,11] which is based on real-space, Keldysh nonequilibrium Green's function (NEGF) formalism combined with density functional theory (DFT). The basic idea of the NEGF-DFT formalism [10] is to calculate device Hamiltonian and electronic structure by DFT, populate this electronic structure using NEGF which properly takes into account nonequilibrium q...

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confidence: 77%

First Principles Modeling of Tunnel Magnetoresistance ofFe/MgO/FeTrilayers

et al. 2006

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“…This is correct for a perfect epitaxial junction. 8,9 However, when an interfacial intermixing is present metal-insulator gap states ͑MIGS͒ may form at the interface, and such states determine ultimately the position of E F in the MgO gap. 10 Without detailed knowledge of the nature of the MIGS, the position of E F in the MgO gap cannot be determined from first principles.…”

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confidence: 99%

Theory of tunneling magnetoresistance in a disorderedFe∕MgO∕Fe(001)junction

Mathon

Umerski

2006

Phys. Rev. B

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“…The barrier height is almost consistent with the experimental value. 78) Since the bond length of O-O in NaCl type MgO is about the same with the lattice constant of bcc Fe, we assume for simplicity that the lattice constant of MgO is √ 2 times as long as that of Fe. In (001)-stacking, Fe lattice is rotated by π/4 relative to MgO lattice.…”

Section: Model and Methodsmentioning

confidence: 99%

“…This assumption is supported by experimental and theoretical works. 74,[78][79][80][81] Transfer integrals at interface between Fe and MgO are calculated by Harrison's method. 82) As for the randomness in MgO, we consider distortion of the perfect MgO lattice.…”

Section: Model and Methodsmentioning

confidence: 99%

Theory of Tunnel Magnetoresistance

Itoh¹,

Inoue²

2006

J. Magn. Soc. Jpn.

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We present a review of theories of tunnel magnetoresistance (TMR) putting an emphasis on the role of electron scattering due to randomness. We adopt the linear response theory and generalize the conductance formula to calculate the electrical conductance in layered structures. The effect of randomness is treated in the coherent potential approximation and/or direct numerical simulation. Because the momentum conservation parallel to the junction planes does not hold in the presence of randomness, number of tunneling path through the barrier increases. Using a simple tight-binding model, we demonstrate first how the tunnel conductance and TMR are influenced by the randomness and by the shape of the Fermi surface of the metallic electrodes. The theory is applied to epitaxial tunnel junctions of Fe/MgO/Fe. It is shown that the basic concept of tunneling in the presence of randomness is also hold in realistic junctions. Magnetoresistance of tunnel junctions with semimetals and those with manganites is studied to clarify the effect of their electronic structures and interaction on TMR.

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Single-crystal magnetotunnel junctions

Cited by 122 publications

References 16 publications

First Principles Modeling of Tunnel Magnetoresistance ofFe/MgO/FeTrilayers

First Principles Modeling of Tunnel Magnetoresistance ofFe/MgO/FeTrilayers

Theory of tunneling magnetoresistance in a disorderedFe∕MgO∕Fe(001)junction

Theory of Tunnel Magnetoresistance

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