Observation of full shot noise in CoFeB/MgO/CoFeB-based magnetic tunneling junctions

Sekiguchi, Koji; Arakawa, Tomoyuki; Yamauchi, Yoshiaki; Chida, Kensaku; Yamada, Masaki; Takahashi, Hiromasa; Chiba, Daichi; Kobayashi, Kensuke; Ono, Teruo

doi:10.1063/1.3456548

Cited by 21 publications

(30 citation statements)

References 25 publications

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“…28 Furthermore, even though an OV concentration of around 5% suppresses the Fano factor, a further increase leads to a remarkable recovery of the full shot noise. The full shot noise observed in earlier experiments 20,21 is therefore consistent with higher disorder. Notice that when the OVs are in the middle of barrier, conductance decreases.…”

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confidence: 73%

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Shot noise in magnetic tunnel junctions from first principles

Xia

Bauer

2012

Phys. Rev. B

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We compute the shot noise in ballistic and disordered Fe|MgO|Fe tunnel junctions by a wave-function-matching method. For tunnel barriers with 5 atomic layers we find a suppression of the Fano factor as a function of the magnetic configuration. In the antiparallel configuration the shot noise is full up to a threshold bias that indicates the onset of resonant tunneling. We find excellent agreement with recent experiments when interface disorder is taken into account. The statistics of electron transport in mesoscopic systems has been the subject of intensive research in the past decades, leading to important and useful insights.1,2 In a two-terminal conductor with a time-dependent current I (t), the simplest measure is the noise poweriωt dt, where I (t) ≡ I (t) − I denotes the instantaneous fluctuation from the average current and · · · is a time and statistical average. The shot noise S is the zero frequency limit of the noise power when the applied voltage |eV | is sufficiently larger than the thermal energy k B T . The classical shot noise characterized by an uncorrelated Poissonian process is given by the Schottky formula S = 2e I .3 Shot noise contains information about the charge of the elementary excitations, entanglement, the wave versus particle nature of electron transport, and provides a diagnostic for open transport channels. 4 Magnetic tunnel junctions (MTJs) with MgO barriers 5,6 have great potential for applications in magnetic random access memory elements and high-frequency generators. [7][8][9][10] Band structure calculations of isomorphic Fe|MgO|Fe layered structures predicted a large drop in the electric resistance when the relative magnetization direction of the two ferromagnets switches from antiparallel to parallel. 11,12 The subsequently observed large Tunnel Magnetoresistance Ratio (TMR) 5,6 can be explained in terms of the symmetry matching of only the majority-spin states in Fe with the 1 band of MgO, which is by far the least evanescent in the gap. The tunneling ratio of the majority-spin electrons is therefore relatively high while minority-spin states are efficiently filtered out by the MgO barrier. However, a quantitative first-principles description of transport in magnetic tunneling junctions is complicated by defects. The chemical composition of the interface strongly affects the TMR, [13][14][15] and various interfacial defects have been identified to reduce the TMR. [16][17][18] The I-V curves alone cannot discriminate between the possible different origins that reduce the TMR.According to conventional wisdom, shot noise in tunnel junctions is classical, 1 in agreement with earlier experiments.19-21 Recent evidence that shot noise in MTJs is suppressed in the parallel configuration was very surprising. 22In order to resolve this issue we present parameter-free calculations of shot noise in magnetic tunnel junctions. We compute sub-Poissonian shot noise for the parallel magnetic configuration and explain the results in terms of highly transmitting resonant tunneling between stat...

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supporting

confidence: 73%

“…[19][20][21] Recent evidence that shot noise in MTJs is suppressed in the parallel configuration was very surprising. 22 In order to resolve this issue we present parameter-free calculations of shot noise in magnetic tunnel junctions.…”

mentioning

confidence: 99%

Shot noise in magnetic tunnel junctions from first principles

Xia

Bauer

2012

Phys. Rev. B

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“…42 Our computed values have same dependence on spin valve magnet alignment (about a factor of 4-5 higher for antiparallel than parallel configuration) but a factor of 3-4 less than the measured values. There is a simple explanation of the configuration dependence from the quantum approach (see Sec.…”

Section: Current Driven Macro-spin Dynamicssupporting

confidence: 41%

“…Finally, the shot noise measurements 42,43 in STT open up the question whether it is due to the atomic nature of the magnetization recoil from scattering or from that of the current through the tunnel junction not related to the magnetization dynamics. 44 This will be discussed in Sec.…”

Section: Relevant Experimentsmentioning

confidence: 98%

A theory of quantum dynamics of a nanomagnet under excitation

Sham

2013

Spintronics VI

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A quantum treatment of magnetization dynamics of a nanomagnet between a thousand and a million spins may be needed as the magnet interacts with quantum control. The advantage of the all-quantum approach over the classical treatment of magnetization is the accounting for the correlation between the magnet and the control agent and the first-principles source of noise. This supplement to the conference talk will concentrate on an overview of the theory with a presentation of the basic ideas which could have wide applications and illustrations with some results. Details of applications to specific models are or will be published elsewhere. A clear concept of the structure of the ground and excited macrospin states as magnetization rotation states and magnons in the Bloch/Dyson sense gives rise to a consistent theory of the magnetization dynamics of a ferromagnet modeled by the Heisenberg Hamiltonian. An example of quantum control is the spin torque transfer, treated here as a sequence of scatterings of each current electron with the localized electrons of the ferromagnet, yields in each encounter a probability distribution of the magnetization recoil state correlated with each outgoing state of the electron. This picture provides a natural Monte Carlo process for simulation of the dynamics in which the probability is determined by quantum mechanics. The computed results of mean motion, noise and damping of the magnetization will be discussed.

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“…49,[53][54][55] The cross-correlation technique is employed as shown in Fig. 3(a) to minimize the external noise from the cables and the amplifiers.…”

Section: High-frequency Measurementsmentioning

confidence: 99%

Observation of finite excess noise in the voltage-biased quantum Hall regime as a precursor for breakdown

et al. 2013

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We performed noise measurements in a two-dimensional electron gas to investigate the nonequilibrium quantum Hall effect (QHE) state. While excess noise is perfectly suppressed around the zero-biased QHE state reflecting the dissipationless electron transport of the QHE state, considerable finite excess noise is observed in the breakdown regime of the QHE. The noise temperature deduced from the excess noise is found to be of the same order as the energy gap between the highest occupied Landau level and the lowest empty one. Moreover, unexpected finite excess noise is observed at a finite source-drain bias voltage smaller than the onset voltage of the QHE breakdown, which indicates finite dissipation in the QHE state and may be related to the prebreakdown of the QHE.

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Observation of full shot noise in CoFeB/MgO/CoFeB-based magnetic tunneling junctions

Abstract: Evidence for boron diffusion into sub-stoichiometric MgO (001) barriers in CoFeB/MgO-based magnetic tunnel junctions

Cited by 21 publications

References 25 publications

Shot noise in magnetic tunnel junctions from first principles

Shot noise in magnetic tunnel junctions from first principles

A theory of quantum dynamics of a nanomagnet under excitation

Observation of finite excess noise in the voltage-biased quantum Hall regime as a precursor for breakdown

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