First-Principles Theory of Quantum Well Resonance in Double Barrier Magnetic Tunnel Junctions

Wang, Y.; Lu, Zhong-Yi; Zhang, Xiaoguang; Han, X. F.

doi:10.1103/physrevlett.97.087210

Cited by 41 publications

(35 citation statements)

References 16 publications

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“…The well-defined oscillations of the differential conductance indicate the presence of resonant transmission through QWSs formed in the central Fe 2 layer. The observed oscillation period is around 300 mV and is in rough agreement with the predictions for DMTJs with a 5 nm central layer [23]. QWSs are more pronounced for positive biases (when electrons tunnel from the bottom to the upper electrodes) for DMTJ1 and DMTJ2 and, as could be expected from the barrier asymmetry, are more pronounced for negative bias for DMTJ3.…”

supporting

confidence: 86%

“…Double-barrier magnetic tunnel junctions (DMTJs), with either nanoparticles [22,23] or a continuous magnetic layer as the central electrode [24], have some advantages in comparison with MTJs. First, they show an enhanced tunnel magnetoresistance (TMR) [24,25], which additionally reveals oscillations induced by quantum well states (QWSs) [23,26]. Second, spin accumulation in the central layer is expected to substantially enhance spin torque [27,28].…”

mentioning

confidence: 99%

“…Then, the noise was examined for ultrathin (less than 1 nm) MgO barriers, where F ' 0:92 was observed in the parallel state [20,21]. Double-barrier magnetic tunnel junctions (DMTJs), with either nanoparticles [22,23] or a continuous magnetic layer as the central electrode [24], have some advantages in comparison with MTJs. First, they show an enhanced tunnel magnetoresistance (TMR) [24,25], which additionally reveals oscillations induced by quantum well states (QWSs) [23,26].…”

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confidence: 99%

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Controlling Shot Noise in Double-Barrier Magnetic Tunnel Junctions

Cascales¹,

Herranz²,

Aliev³

et al. 2012

Phys. Rev. Lett.

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We demonstrate that shot noise in Fe=MgO=Fe=MgO=Fe double-barrier magnetic tunnel junctions is determined by the relative magnetic configuration of the junction and also by the asymmetry of the barriers. The proposed theoretical model, based on sequential tunneling through the system and including spin relaxation, successfully accounts for the experimental observations for bias voltages below 0.5 V, where the influence of quantum well states is negligible. A weak enhancement of conductance and shot noise, observed at some voltages (especially above 0.5 V), indicates the formation of quantum well states in the middle magnetic layer. As solid-state electronic devices shrink in size, further advances essentially depend on the understanding and control of spontaneous off-equilibrium fluctuations in charge and/or spin currents. Being a consequence of the discrete nature of charge carriers, shot noise (SN) is the only contribution to the noise which survives at low temperatures. Moreover, SN is an excellent tool to investigate the correlations and coherency at the nanoscale, well beyond the capabilities of electron transport [1][2][3][4][5][6][7][8][9]. In the absence of correlations, SN is Poissonian (full shot noise) and its noise power is given by S full ¼ 2eI, where I is the average current and e the electron charge. The Fano factor, F ¼ S exp =S full , represents the experimental SN normalized by the full SN value. It is generally suppressed (F < 1) by electron correlations [1] (quantum and/or Coulomb), but it can also be enhanced (F > 1), e.g., due to tunneling via localized states [10].After the observation of spin dependent transport in Fe=MgO=Fe magnetic tunnel junctions (MTJs) [11,12], MgO-based junctions became important elements of spintronic devices. Moreover, the recent implementation of MgO for an effective spin injection [13,14] revealed a new road for reducing the spin relaxation due to conductivity mismatch [15,16]. The efforts aimed at understanding spin coherency and SN, limited up to now to MTJs, revealed suppressed SN with Al 2 O 3 barriers (0:7 < F < 1) due to sequential tunneling [17] and also in serial MTJ arrays [18]. As for MTJs with MgO barriers, full SN (F ¼ 1) independent of the magnetic state was observed in epitaxial Fe=MgO=Fe [19]. Then, the noise was examined for ultrathin (less than 1 nm) MgO barriers, where F ' 0:92 was observed in the parallel state [20,21]. Double-barrier magnetic tunnel junctions (DMTJs), with either nanoparticles [22,23] or a continuous magnetic layer as the central electrode [24], have some advantages in comparison with MTJs. First, they show an enhanced tunnel magnetoresistance (TMR) [24,25], which additionally reveals oscillations induced by quantum well states (QWSs) [23,26]. Second, spin accumulation in the central layer is expected to substantially enhance spin torque [27,28]. The investigation of the statistics of spin tunneling events in hybrid spintronic devices is of great potential interest also beyond the spintronics community. From a general point o...

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supporting

confidence: 86%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Controlling Shot Noise in Double-Barrier Magnetic Tunnel Junctions

Cascales¹,

Herranz²,

Aliev³

et al. 2012

Phys. Rev. Lett.

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“…Thus, we calculated QW state positions in the energy-thickness plane using the socalled PAM, 26 where electrons inside the CoFeB free layer are confined in a potential well of width t fl [Figs. 1(c) and 1(d)].…”

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Observation of spin-dependent quantum well resonant tunneling in textured CoFeB layers

Teixeira

Costa

Ventura

et al. 2014

Applied Physics Letters

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We report the observation of spin-dependent quantum well (QW) resonant tunneling in textured CoFeB free layers of single MgO magnetic tunnel junctions (MTJs). The inelastic electron tunneling spectroscopy spectra clearly show the presence of resonant oscillations in the parallel configuration, which are related with the appearance of majority-spin Δ1 QW states in the CoFeB free layer. To gain a quantitative understanding, we calculated QW state positions in the voltage-thickness plane using the so-called phase accumulation model (PAM) and compared the PAM solutions with the experimental resonant voltages observed for a set of MTJs with different CoFeB free layer thicknesses (tfl = 1.55, 1.65, 1.95, and 3.0 nm). An overall good agreement between experiment and theory was obtained. An enhancement of the tunnel magnetoresistance with bias is observed in a bias voltage region corresponding to the resonant oscillations.

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“…[1][2][3][4][5] Besides single barrier MTJs (SBMTJs), double barrier MTJs (DBMTJs) have also been extensively studied for the novel physical phenomena and potential applications in spintronic devices. [6][7][8][9][10][11][12][13][14] With a thin ferromagnetic (FM) layer sandwiched by two MgO layers, quantum well oscillations and Coulomb blockade phenomena have been reported. 7,8,[12][13][14] Compared with SBMTJs, DBMTJs have larger V 1/2 (voltage where TMR decreases to its half maximum value), 6,[9][10][11] which is desirable for practical applications.…”

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Tunneling processes in asymmetric double barrier magnetic tunnel junctions with a thin top MgO layer

Feng

et al. 2013

Journal of Applied Physics

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Dynamic conductance dI/dV and inelastic electron tunneling spectroscopy (IETS) d 2 I/dV 2 have been measured at different temperatures for double barrier magnetic tunnel junctions with a thin top MgO layer. The resistance in the antiparallel state exhibits a normal tunnel-like behavior, while the resistance in the parallel state shows metallic-like transport, indicating the presence of pinholes in the thin top MgO layer. Three IETS peaks are the zero-bias anomaly, interface magnons, and barrier phonons in both the parallel and antiparallel states. The zero-bias anomaly is the strongest peak in the parallel state and its intensity decreases with temperature. The magnon has the largest intensity in the antiparallel state and its intensity also decreases with temperature. The origins of the dips and peaks in the dI/dV-V curve are also discussed. V C 2013 AIP Publishing LLC.

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First-Principles Theory of Quantum Well Resonance in Double Barrier Magnetic Tunnel Junctions

Cited by 41 publications

References 16 publications

Controlling Shot Noise in Double-Barrier Magnetic Tunnel Junctions

Controlling Shot Noise in Double-Barrier Magnetic Tunnel Junctions

Observation of spin-dependent quantum well resonant tunneling in textured CoFeB layers

Tunneling processes in asymmetric double barrier magnetic tunnel junctions with a thin top MgO layer

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