Validity of the Julliere model of spin-dependent tunneling

MacLaren, J. M.; Zhang, X.-G.; Butler, W. H.

doi:10.1103/physrevb.56.11827

Cited by 141 publications

(106 citation statements)

References 10 publications

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“…This is a typical feature of the Slonczewski approximation [Eq. (14)] which has also been observed in theoretical investigations of the TMR [39]. It is intrinsic to the derivation of Eq.…”

Section: Resultsmentioning

confidence: 97%

Tunneling magnetothermopower in magnetic tunnel junctions

2014

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Thermally induced spin-dependent transport across magnetic tunnel junctions (MTJs) is theoretically investigated. We analyze the thermal analog of Slonczewski's model (as well as its limiting case-Julliere's model) of tunneling magnetoresistance and obtain analytical expressions for the junction thermopower and the tunneling magnetothermopower (TMT). The analytical model is tested numerically for the special case of an Al 2 O 3 -based MTJ, for which we analyze the dependence of the thermopower and TMT on the relative magnetization orientations, as well as on the barrier height and thickness. We show that at a certain barrier height TMT vanishes, separating the region of positive and negative TMT. As its electrical prototype, this thermal spin transport model should serve as a phenomenological benchmark for analyzing experimental and first-principles calculations of thermopower in magnetic tunnel junctions. The analytical expressions can be used as a first estimate of the magnetothermopower of the junctions using ab initio band structure data of the junction ferromagnets.

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“…This is a typical feature of the Slonczewski approximation [Eq. (14)] which has also been observed in theoretical investigations of the TMR [39]. It is intrinsic to the derivation of Eq.…”

Section: Resultsmentioning

confidence: 97%

Tunneling magnetothermopower in magnetic tunnel junctions

2014

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“…MacLaren et al [7] was amongst the first to illustrate the shortcomings of the Jullière model. Furthermore, using first principles calculations for epitaxial Fe(100)/MgO(100)/Fe(100) trilayers, Butler et al [8] showed how the decay of the evanescent wavefunction into the barrier depends critically on its symmetry, which has a dramatic influence on the calculated TMR value.…”

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confidence: 99%

The role of interfaces in organic spin valves revealed through spectroscopic and transport measurements

Drew

Szulczewski

Nuccio

et al. 2011

Physica Status Solidi (b)

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Interfaces between dissimilar materials are critical to the performance of many electronic devices. In electrical devices where the active transport is through an organic semiconductor (OSC) layer there are metallic electrodes to supply and remove the charge carriers. At metal/molecule and molecule/metal interfaces the electrical contact is usually not Ohmic. As a result, in most metal-organic semiconductors-metal devices charge injection is mainly governed by tunneling across the barriers. When the metal electrodes are ferromagnetic the density of occupied and unoccupied electronic states is spindependent, which presents further subtleties to the electron transfer. In this article we summarize some of the important experimental results that have advanced our understanding of spin-polarized electron transfer across ferromagnetic metal (FM)/OSC interfaces. In particular, we highlight key spectroscopic studies that have revealed insights into the nature of the electronic structure between OSCs and FMs, in particular between Alq 3 and Co and Fe surfaces. We discuss the relationship between energy level diagrams for these systems and transport measurements made on spin-valve devices.

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“…The understanding of the TMR and of the electronic structure has not progressed equally quickly. Model calculations 3,4 have shed light on various aspects of the effect, but only recently have ab initio calculations of the electronic structure and the spindependent transport been reported. [5][6][7][8] In this paper, we will consider the tunneling through epitaxial junctions, which are characterized by two-dimensional periodicity.…”

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confidence: 99%

Effects of resonant interface states on tunneling magnetoresistance

et al. 2002

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Based on model and ab initio calculations we discuss the effect of resonant interface states on the conductance of epitaxial tunnel junctions. In particular we show that the ''hot spots'' found by several groups in ab initio calculations of symmetrical barriers of the k ʈ -resolved conductance can be explained by the formation of bonding and antibonding hybrids between the interface states on both sides of the barrier. If the resonance condition for these hybrid states is met, the electron tunnels through the barrier without attenuation. Even when both hybrid states move together and form a single resonance, strongly enhanced transmission is still observed. The effect explains why, for intermediate barrier thicknesses, the tunneling conductance can be dominated by interface states, although hot spots only occur in a tiny fraction of the surface Brillouin zone. DOI: 10.1103/PhysRevB.65.064425 PACS number͑s͒: 72.25.Ϫb, 73.20.Ϫr, 73.40.Rw, 73.40.Gk The tunneling magnetoresistance ͑TMR͒ of magnetic tunnel junctions consisting of ferromagnet͉insulator͉ferro-magnet layers has attracted a strong scientific interest, partly due to their potential application as magnetic random access memories. Miyazaki and Tezuka 1 and Moodera et al. 2 were able to obtain TMR ratios up to 20% in room-temperature experiments and recently room-temperature values of more than 50% were reported by various groups. The understanding of the TMR and of the electronic structure has not progressed equally quickly. Model calculations 3,4 have shed light on various aspects of the effect, but only recently have ab initio calculations of the electronic structure and the spindependent transport been reported. [5][6][7][8] In this paper, we will consider the tunneling through epitaxial junctions, which are characterized by two-dimensional periodicity. Here recent ab initio calculations of the k ʈ -resolved conductance show a very interesting phenomenon: for certain discrete k ʈ values ''hot spots'' or ''spikes'' appear in the transmitted intensity, showing that electrons with such k ʈ values can apparently tunnel through the junction with no or very little attenuation while all other states are very strongly damped. [9][10][11] This effect occurs only in the minority band of the ferromagnet and only for ferromagnetic coupling. If present, it can dominate the tunnel characteristics for intermediate thicknesses. For large thicknesses, in the asymptotic limit, the behavior is determined by the complex band structure of the insulator, 12 i.e., by those metal-inducedgap states, which have the smallest imaginary part of the perpendicular component k z of the Bloch vector. An example for such hot spots is given in Fig. 1, showing the results of ab initio Korringa-Kohn-Rostoker calculations for a junction consisting of two fcc Co͑001͒ half-crystals separated by 4 monolayers ͑ML͒ of vacuum. The results are based on density-functional theory in the local-density approximation and the Landauer formula for the conductance. We have chosen a vacuum layer as the ...

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Validity of the Julliere model of spin-dependent tunneling

Cited by 141 publications

References 10 publications

Tunneling magnetothermopower in magnetic tunnel junctions

Tunneling magnetothermopower in magnetic tunnel junctions

The role of interfaces in organic spin valves revealed through spectroscopic and transport measurements

Effects of resonant interface states on tunneling magnetoresistance

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