Voltage-controlled magnetic anisotropy in an ultrathin Ir-doped Fe layer with
          a CoFe termination layer

Nozaki, Takayuki; Endo, Masaki; Tsujikawa, Motokazu; Yamamoto, Tomohiko; Nozaki, Tomohiro; Konoto, Makoto; Ohmori, Hiroyuki; Higo, Y.; Fukushima, Akio; Hosomi, Masanori; Shirai, Masamitsu; Suzuki, Y.; Yuasa, Shinji

doi:10.1063/1.5132626

Cited by 54 publications

(45 citation statements)

References 41 publications

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“…Recently, Nozaki et al demonstrated a significant enhancement in the VCMA effect, as high as 350 fJ/Vm, via engineering of the FM/oxide interface in an ultrathin Ir-doped Fe/MgO structures with a CoFe termination layer. 45 Employing an ionic mechanism to control the PMA could potentially result in even stronger modulation of the damping and possibly also non-volatile storage of different damping values. 46 Further improvement in the damping modulation should also be possible via optimizing the device layout.…”

Section: Discussionmentioning

confidence: 99%

Giant voltage-controlled modulation of spin Hall nano-oscillator damping

et al. 2020

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Spin Hall nano-oscillators (SHNOs) are emerging spintronic devices for microwave signal generation and oscillator-based neuromorphic computing combining nano-scale footprint, fast and ultra-wide microwave frequency tunability, CMOS compatibility, and strong non-linear properties providing robust large-scale mutual synchronization in chains and two-dimensional arrays. While SHNOs can be tuned via magnetic fields and the drive current, neither approach is conducive to individual SHNO control in large arrays. Here, we demonstrate electrically gated W/CoFeB/MgO nano-constrictions in which the voltage-dependent perpendicular magnetic anisotropy tunes the frequency and, thanks to nano-constriction geometry, drastically modifies the spin-wave localization in the constriction region resulting in a giant 42% variation of the effective damping over four volts. As a consequence, the SHNO threshold current can be strongly tuned. Our demonstration adds key functionality to nano-constriction SHNOs and paves the way for energy-efficient control of individual oscillators in SHNO chains and arrays for neuromorphic computing.

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Section: Discussionmentioning

confidence: 99%

Giant voltage-controlled modulation of spin Hall nano-oscillator damping

et al. 2020

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“…For example, one can achieve I eff = 170 μA using the standard material in SOT MRAM technology, such as tungsten, with θ SH = −0.45 [34]. Correspondingly, ξ = 300 fJ/Vm is needed, which can be implemented by appropriate interface engineering [35]. For comparison, these values are much more relaxed than the requirements for SOT MRAM (|θ SH | > 1.6) and for VCMA MRAM (ξ > 800 fJ/Vm, considering t MgO = 1.5 nm at μ 0 H x = 0 mT) of the same .…”

Section: A Device-scaling Criteriamentioning

confidence: 99%

Voltage-Gate-Assisted Spin-Orbit-Torque Magnetic Random-Access Memory for High-Density and Low-Power Embedded Applications

Garello

Kim

et al. 2021

Phys. Rev. Applied

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The voltage-gate-assisted spin-orbit-torque (VGSOT) writing scheme combines the advantages from voltage control of magnetic anisotropy (VCMA) and spin-orbit-torque (SOT) effects, enabling multiple benefits for magnetic random-access-memory (MRAM) applications. In this work, we give a complete description of the VGSOT writing properties on perpendicular magnetic tunnel junction (PMTJ) devices, and we propose a detailed methodology for their electrical characterization. The impact of gate assistance on the SOT switching characteristics is investigated using electrical pulses down to 400 ps. The VCMA coefficient (ξ ) extracted from the current-switching scheme is found to be the same as that from the magnetic-field-switch method, which is in the order of 15 fJ/Vm for 80-150-nm devices. Moreover, as expected from the pure electronic VCMA effect, ξ is revealed to be independent of the writing speed and gate length. We observe that SOT switching current characteristics are modified linearly with gate voltage (V g ), similar to that for the magnetic properties. We interpret this linear behavior as the direct modification of perpendicular magnetic anisotropy induced by VCMA. At V g = 1 V, the SOT write current is decreased by 25%, corresponding to a 45% reduction in total energy down to 30 fJ/bit at 400 ps speed for the 80-nm devices used in this study. To test the operation reliability, we investigate the gate-SOT pulse configurations and overlays, and we find that an extended gate duration is able to preserve maximized gate benefit and selectivity. Furthermore, the device-scaling criteria are proposed, and we reveal that the VGSOT scheme is of great interest, as it can mitigate the complex material requirements of achieving high SOT and VCMA parameters for scaled MTJs. Finally, we perform design-to-technology co-optimization analysis to show that VGSOT MRAM can enable high-density arrays close to two-terminal geometries, with high-speed performance and low-power operation, showing great potential for embedded memories as well as in memory computing applications at advanced technology nodes.

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“…The voltage control of magnetic anisotropy (VCMA) effect 2 , 3 and VCMA-induced precessional magnetization switching 4 , 5 , which are the core technologies of the voltage-controlled MRAM, have been extensively investigated, especially for bcc-Fe/MgO-based systems 6 – 9 , because of the high compatibility with MRAM. Regarding the purely-electronic VCMA effect, a VCMA coefficient of approximately 350 fJ/Vm has been realized for the epitaxial Cr/Fe/Ir/FeCo/MgO structure by precise control of the film structure using the molecular beam epitaxy (MBE) technique 10 , 11 . However, further enhancement of the VCMA coefficient is demanded.…”

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confidence: 99%

Large voltage-induced coercivity change in Pt/Co/CoO/amorphous TiOx structure and heavy metal insertion effect

Nozaki

Tamaru

Konoto

et al. 2021

Sci Rep

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There is urgent need for spintronics materials exhibiting a large voltage modulation effect to fulfill the great demand for high-speed, low-power-consumption information processing systems. Fcc-Co (111)-based systems are a promising option for research on the voltage effect, on account of their large perpendicular magnetic anisotropy (PMA) and high degree of freedom in structure. Aiming to observe a large voltage effect in a fcc-Co (111)-based system at room temperature, we investigated the voltage-induced coercivity (Hc) change of perpendicularly magnetized Pt/heavy metal/Co/CoO/amorphous TiOx structures. The thin CoO layer in the structure was the result of the surface oxidation of Co. We observed a large voltage-induced Hc change of 20.2 mT by applying 2 V (0.32 V/nm) to a sample without heavy metal insertion, and an Hc change of 15.4 mT by applying 1.8 V (0.29 V/nm) to an Ir-inserted sample. The relative thick Co thickness, Co surface oxidation, and large dielectric constant of TiOx layer could be related to the large voltage-induced Hc change. Furthermore, we demonstrated the separate adjustment of Hc and a voltage-induced Hc change by utilizing both upper and lower interfaces of Co.

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Voltage-controlled magnetic anisotropy in an ultrathin Ir-doped Fe layer with a CoFe termination layer

Cited by 54 publications

References 41 publications

Giant voltage-controlled modulation of spin Hall nano-oscillator damping

Giant voltage-controlled modulation of spin Hall nano-oscillator damping

Voltage-Gate-Assisted Spin-Orbit-Torque Magnetic Random-Access Memory for High-Density and Low-Power Embedded Applications

Large voltage-induced coercivity change in Pt/Co/CoO/amorphous TiOx structure and heavy metal insertion effect

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