Electron tunneling between ferromagnetic films

Maekawa, Sadamichi; Gäfvert, U.

doi:10.1109/tmag.1982.1061834

Cited by 383 publications

(165 citation statements)

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“…In contrast, Inoue and Maekawa 25 assume that the tunneling conductance in the dielectric regime can be derived from the classical expression for the spindependent tunneling in FM/I/FM junctions given by Landauer 28 and Maekawa and Gäfvert. 29 24 which was not predicted by any of the two models, and needed the occurrence of higherorder tunneling processes. Granular solids display a broad particle size distribution such that the gross simplification of the Inoue-Maekawa model 25 is not to take into account tunneling between grains of different sizes.…”

Section: Introductionmentioning

confidence: 80%

Tunneling magnetoresistance inCo−ZrO2granular thin films

et al. 2006

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Granular films composed of well defined nanometric Co particles embedded in an insulating ZrO 2 matrix were prepared by pulsed laser depositon in a wide range of Co volume concentrations ͑0.15Ͻ x Ͻ 0.43͒. High-resolution transmission electron microscopy ͑TEM͒ showed very sharp interfaces between the crystalline particles and the amorphous matrix. Narrow particle size distributions were determined from TEM and by fitting the low-field magnetic susceptibility and isothermal magnetization in the paramagnetic regime to a distribution of Langevin functions. The magnetic particle size varies little for Co volume concentrations x Ͻ 0.32 and increases as the percolation limit is approached. The tunneling magnetoresistance ͑TMR͒ was successfully reproduced using the Inoue-Maekawa model. The maximum value of TMR was temperatureindependent within 50-300 K, and largely increased at low T, suggesting the occurrence of higher-order tunneling processes. Consequently, the tunneling conductance and TMR in clean granular metals are dominated by the Coulomb gap and the inherent particle size distribution.

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Section: Introductionmentioning

confidence: 80%

Tunneling magnetoresistance inCo−ZrO2granular thin films

et al. 2006

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“…The TMR in tunnel junctions with ferromagnetic electrodes [18,19] and magnetic granular films [10] is another attractive topic. Recently, the TMR oscillations in asymmetric double tunnel junctions with ferromagnetic electrodes have been studied [20,21].…”

Section: (D)mentioning

confidence: 99%

Coulomb staircase in STM current through granular films

et al. 2000

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The electron transport through an array of tunnel junctions consisting of an STM tip and a granular film is studied both theoretically and experimentally. When the tunnel resistance between the tip and a granule on the surface is much larger than those between granules, a bottleneck of the tunneling current is created in the array. It is shown that the period of the Coulomb staircase(CS) is given by the capacitance at the bottleneck. Our STM experiments on Co-Al-O granular films show the CS with a single period at room temperature. This provides a new possibility for single-electron-spinelectronic devices at room temperature.Charging effects on single electron tunneling such as Coulomb blockade and Coulomb oscillation have attracted much interest [1]. Recent advances in nanotechnology enable us to fabricate small tunnel junctions where charging effects play an essential role. The I-V characteristics for double tunnel junction systems have been extensively studied, where the step-like structure called Coulomb staircase(CS) is observed when the resistances between the junctions are not equal [1]. For these asymmetric double junction systems, the junction with a large resistance behaves like a bottleneck of the tunneling current and the central island is charged through the other junction up to the maximum charge. The tunneling current jumps when the maximum charge changes. Recently, the CS has been observed by using a tip of scanning tunneling microscope(STM) of nanometer-size in highly resistive granular films [2-5] as well as metaldroplet systems [6,7]. For a granular film, which is considered to be an array of tunnel junctions, the observed CS implies that a bottleneck exists in the conducting paths. However, the physics behind the CS in a granular film is not clear because it contains many granules with different size and the conducting path may form a three-dimensional network in a thick granular film.Bar-Sadeh et al. have studied the STM current through a nonmagnetic granular film, Au-Al 2 O 3 , by using the cryogenic STM [2,3]. They observed the CS at temperatures T = 4.2 and 78 K, and analyzed the experimental data by using a triple barrier model. They assumed that the rate for tunneling between two granules is small and the number of excess electrons in each granule is treated independently. Because of these assumptions, the CS was given by the superposition of two different periods in their model: one was determined by the tunnel process between the STM tip and a granule, the other between another granule and the base electrode. On the contrary, as we will show later, the CS has a single period which is determined by the capacitance at the bottleneck.In this Letter, we study the electron transport through an array of tunnel junctions consisting of an STM tip and a granular film both theoretically and experimentally. In this system, we can vary the tunnel resistance between the tip and a granule on the surface by changing the distance between them. When the tunnel resistance between the tip and a granule ...

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“…9,10 The physical principle that underlies the MR in both cases is a spin-dependent electric charge transfer between two magnetized electrodes or grains via tunneling effect. 11,12 This effect is called tunneling MR ͑TMR͒, and the tunneling probability depends on the relative orientation of magnetization of the electrodes or grains. 13 Experimentally TMR ratios up to 180% in fully epitaxial Fe͑001͒/ MgO͑001͒/Fe͑001͒ junction were found at room temperature, 7 and first-principles calculations predict even higher values.…”

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confidence: 99%

Tunneling magnetoresistance in Fe/MgO granular multilayers

García-García

Vovk

Pardo

et al. 2010

Journal of Applied Physics

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We have investigated the transport and magnetotransport properties in Fe/MgO multilayers around the Fe percolation threshold as a function of the temperature and the nominal thickness of iron layer ͑t͒. Electrical resistivity measurements allowed us to disclose the charge transport mechanisms involved, which are closely related to the degree of discontinuity in the Fe layers. The samples with Fe thickness below percolation threshold ͑t ϳ 0.8 nm͒ exhibit isotropic magnetoresistance ͑MR͒, which can be understood considering spin-polarized electron tunneling between nanometer-sized, superparamagnetic Fe grains. The MR ratio increases with decreasing temperature from ϳ3% at room temperature to ϳ10% at 30 K. The temperature dependence of MR can be explained satisfactorily in terms of a modified Mitani's model. © 2010 American Institute of Physics. ͓doi:10.1063/1.3298504͔A new generation of devices combining the advantages of semiconductor electronics with spin-dependent transport is emerging as a consequence of the strong potential for magnetoelectronic applications, such as storage media, sensors, and potentiometers. 1 The interest in the development of these spintronic devices inspired the search for new materials in the nanometric length scale, where the magnetic and transport properties differ substantially from those of the bulk. Among them we can mention granular cermets-in which nanometer-sized magnetic metallic particles are embedded in an insulating matrix. [2][3][4][5] Discontinuous metal-insulator multilayers ͑DMIMs͒ are a special kind of granular cermets where the metallic particles are located not randomly but in layers, and this arrangement causes the enhancement of the low-field dependence and relatively high magnetoresistance ͑MR͒ ratios at room temperature. 6 DMIMs are easier to prepare than planar, epitaxial magnetic tunnel junctions ͑MTJs͒ showing huge MR values, 7,8 but strongly reduced by structural defects at interfaces. 9,10 The physical principle that underlies the MR in both cases is a spin-dependent electric charge transfer between two magnetized electrodes or grains via tunneling effect. 11,12 This effect is called tunneling MR ͑TMR͒, and the tunneling probability depends on the relative orientation of magnetization of the electrodes or grains. 13 Experimentally TMR ratios up to 180% in fully epitaxial Fe͑001͒/ MgO͑001͒/Fe͑001͒ junction were found at room temperature, 7 and first-principles calculations predict even higher values. 14 Despite extensive research on planar Fe/ MgO/Fe MTJs, little attention has been paid to Fe/MgO granular cermets. 15,16 In this paper we present our results on the magnetotransport properties of Fe/MgO DMIMs prepared by pulsed laser deposition ͑PLD͒.Polycrystalline ͓Fe͑t͒ / MgO͑3 nm͔͒ N multilayers with 0.4 nmՅ t Յ 1.5 nm were deposited by PLD on glass substrates. The preparation procedure was reported in detail elsewhere. 16 Electrical resistance and MR measurements were carried out using the four-point method in the temperature range 30-295 K and in-plane app...

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Electron tunneling between ferromagnetic films

Cited by 383 publications

References 6 publications

Tunneling magnetoresistance inCo−ZrO2granular thin films

Tunneling magnetoresistance inCo−ZrO2granular thin films

Coulomb staircase in STM current through granular films

Tunneling magnetoresistance in Fe/MgO granular multilayers

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