Properties of magnetic tunnel junctions with a MgO/CoFeB/Ta/CoFeB/MgO recording structure down to junction diameter of 11 nm

Sato, Hideo; Enobio, Eli Christopher I.; Yamanouchi, Michihiko; Ikeda, Shoji; Fukami, Shunsuke; Kanai, Shun; Matsukura, F.; Ohno, Hideo

doi:10.1063/1.4892924

Cited by 261 publications

(182 citation statements)

References 24 publications

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“…In our 50 × 150nm superparamagnetic tunnel junctions, we identified that the switching occurs through nucleation and propagation of a magnetic domain, probably seeded by fluctuations in a subset of grains within it 31 (supplementary information S3). By contrast, recent experiments on perpendicular magnetic anisotropy (PMA) magnetic tunnel junctions have shown that aggressively scaled devices (diameters smaller than 35nm) switch at the scale of the whole volume 34 . Therefore, in the context of random number generators, extreme scaling of the nanodevices appears as providential, as smaller volumes and areas are directly linked to a lower magnetization stability of the free magnet 40 , increasing random bit generation speed exponentially.…”

Section: Scaling Capabilities Of the Random Number Generators In mentioning

confidence: 95%

“…We see that the resistance follows two-state fluctuations analogous to a random telegraph signal. The mean frequency of fluctuations is strongly related to the shape and material properties of the junction 34 . Fig.…”

Section: Exploiting the Stochastic Behavior Of Superparamagnetic mentioning

confidence: 99%

“…t is derived as a function of the device diameter D, where t = 1.6nm is the free magnet thickness and the effective anisotropy K ef f (D) is derived considering interfacial anisotropy and bulk anisotropies, using experimental values from 34 . Fig.…”

Section: Scaling Capabilities Of the Random Number Generators In mentioning

confidence: 99%

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Low-Energy Truly Random Number Generation with Superparamagnetic Tunnel Junctions for Unconventional Computing

et al. 2017

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Low-energy random number generation is critical for many emerging computing schemes proposed to complement or replace von Neumann architectures. However, current random number generators are always associated with an energy cost that is prohibitive for these computing schemes. In this paper, we introduce random number bit generation based on specific nanodevices: superparamagnetic tunnel junctions. We experimentally demonstrate high quality random bit generation that represents orders-of-magnitude improvements in energy efficiency compared to current solutions. We show that the random generation speed improves with nanodevice scaling, and investigate the impact of temperature, magnetic field and crosstalk. Finally, we show how alternative computing schemes can be implemented using superparamagentic tunnel junctions as random number generators. These results open the way for fabricating efficient hardware computing devices leveraging stochasticity, and highlight a novel use for emerging nanodevices.

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Section: Scaling Capabilities Of the Random Number Generators In mentioning

confidence: 95%

Section: Exploiting the Stochastic Behavior Of Superparamagnetic mentioning

confidence: 99%

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Low-Energy Truly Random Number Generation with Superparamagnetic Tunnel Junctions for Unconventional Computing

et al. 2017

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“…K eff can often be improved by introducing a second CoFeB/MgO interface in more complicated MgO/CoFeB/Ta/CoFeB/MgO structures [4]. Nevertheless, it has been shown that even the optimized MTJ structure is unstable for dimensions below 30 nm [5]. Novel materials with strong magnetocrystalline or strain-induced PMA are needed.…”

Section: Introductionmentioning

confidence: 99%

Structure, site-specific magnetism, and magnetotransport properties of epitaxial D022 -structure Mn2FexGa thin

et al. 2017

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Ferrimagnetic Mn 2 Fe x Ga (0.26 x 1.12) thin films have been characterized by x-ray diffraction, magnetometry, x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and Mössbauer spectroscopy with the aim of determining the structure and site-specific magnetism of this tetragonal, D0 22 -structure Heusler compound. High-quality epitaxial films with low root-mean-square surface roughness (∼0.6 nm) are grown by magnetron cosputtering. The tetragonal distortion induces strong perpendicular magnetic anisotropy along the c axis with a typical coercive field μ 0 H ∼ 0.8 T and an anisotropy field ranging from 6 to 8 T. On increasing the Fe content x, substantial uniaxial anisotropy, K u 1.0 MJ m −3 , can be maintained over the full x range, while the magnetization of the compound is reduced from 400 to 280 kA m −1 . The total magnetization is almost entirelygiven by the sum of the spin moments originating from the ferrimagnetic Mn and Fe sublattices, with the latter being coupled ferromagnetically to one of the former. The orbital magnetic moments are practically quenched and have negligible contributions to the magnetization. The films with x = 0.73 exhibit an anomalous Hall angle of 2.5% and a Fermi-level spin polarization above 51%, as measured by point contact Andreev reflection. The Fe-substituted Mn 2 Ga films are tunable with a unique combination of high anisotropy, low magnetization, appreciable spin polarization, and low surface roughness, making them strong candidates for thermally stable spin-transfer-torque switching nanomagnets with lateral dimensions down to 10 nm.

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“…Magnetostatic interaction between layers is largely offset by the exchange and not included here. The objective of this design is to maximize the switching efficiency ξ-the existing figure of merit: [8][9][10] …”

Section: Simulation Modelmentioning

confidence: 99%

Dual referenced composite free layer design optimization for improving switching efficiency of spin-transfer torque RAM

Bell

Victora

2017

AIP Advances

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We present a detailed numerical analysis of switching efficiency for the recently proposed dual referenced composite free layer structure with respect to Gilbert damping. Low anisotropy assistive layers enable reduction of Gilbert damping and an increase of partial spin polarization within those low anisotropy layers—not feasible with single layer structures that require high anisotropy for thermal stability. When the damping of the soft layers is ultra-low, an efficiency (kBT/μA) of 8.1 is achieved for the composite structure with perpendicular anisotropy. This represents an improvement of 286% and 913% relative to the state-of-the-art dual-referenced and conventional STT-RAM cells, respectively. Results for structures with longitudinal anisotropy are also presented. A linear calculation of the STT polarization pre-factor is also described that captures all reflections.

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Properties of magnetic tunnel junctions with a MgO/CoFeB/Ta/CoFeB/MgO recording structure down to junction diameter of 11 nm

Cited by 261 publications

References 24 publications

Low-Energy Truly Random Number Generation with Superparamagnetic Tunnel Junctions for Unconventional Computing

Low-Energy Truly Random Number Generation with Superparamagnetic Tunnel Junctions for Unconventional Computing

Structure, site-specific magnetism, and magnetotransport properties of epitaxial D022 -structure Mn2FexGa thin

Dual referenced composite free layer design optimization for improving switching efficiency of spin-transfer torque RAM

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