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Vladimir Nikitin

Bio: Vladimir Nikitin is an academic researcher from Samsung. The author has contributed to research in topics: Spin-transfer torque & Layer (electronics). The author has an hindex of 25, co-authored 108 publications receiving 3168 citations. Previous affiliations of Vladimir Nikitin include Hitachi & University of California, Santa Barbara.


Papers
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Journal ArticleDOI
TL;DR: The fundamental physical principles of STT-MRAM operation are discussed, covering the range from device level to chip array performance, and methodology for its development.
Abstract: For reliable operation, individual cells of an STT-MRAM memory array must meet specific requirements on their performance. In this work we review some of these requirements and discuss the fundamental physical principles of STT-MRAM operation, covering the range from device level to chip array performance, and methodology for its development.

448 citations

Journal ArticleDOI
TL;DR: The progress of the work on device design, material improvement, wafer processing, integration with CMOS, and testing for a demonstration STT-RAM test chip are reported, and projections based on modeling of the future characteristics of STt-RAM are projected.
Abstract: Spin-transfer torque random access memory (STT-RAM) is a potentially revolutionary universal memory technology that combines the capacity and cost benefits of DRAM, the fast read and write performance of SRAM, the non-volatility of Flash, and essentially unlimited endurance. In order to realize a small cell size, high speed and achieve a fully functional STT-RAM chip, the MgO-barrier magnetic tunnel junctions (MTJ) used as the core storage and readout element must meet a set of performance requirements on switching current density, voltage, magneto-resistance ratio (MR), resistance-area product (RA), thermal stability factor (?) , switching current distribution, read resistance distribution and reliability. In this paper, we report the progress of our work on device design, material improvement, wafer processing, integration with CMOS, and testing for a demonstration STT-RAM test chip, and projections based on modeling of the future characteristics of STT-RAM.

401 citations

Journal ArticleDOI
TL;DR: In this article, the authors identify the best conditions for efficient domain-wall motion by spin-orbit torques originating from the spin Hall effect or Rashba effect and demonstrate that the effect depends critically on the domain wall configuration, the current injection scheme, and the symmetry of the spinorbit torque.
Abstract: In our numerical study, we identify the best conditions for efficient domain-wall motion by spin-orbit torques originating from the spin Hall effect or Rashba effect. We demonstrate that the effect depends critically on the domain-wall configuration, the current injection scheme, and the symmetry of the spin-orbit torque. The best identified configuration corresponds to a N\'eel wall driven by the spin Hall effect in a narrow strip with perpendicular magnetic anisotropy. In this case, the domain-wall velocity can be a factor of 10 larger than that for the conventional current-in-plane spin-transfer torque.

391 citations

Journal ArticleDOI
TL;DR: It is shown that in-plane STT-MRAM technology, particularly the DMTJ design, is a mature technology that meets all conventional requirements for an STT -MRAM cell to be a nonvolatile solution matching DRAM and/or SRAM drive circuitry.
Abstract: Spin-transfer torque magnetic random access memory (STT-MRAM) is a novel, magnetic memory technology that leverages the base platform established by an existing 100pnm node memory product called MRAM to enable a scalable nonvolatile memory solution for advanced process nodes. STT-MRAM features fast read and write times, small cell sizes of 6F2 and potentially even smaller, and compatibility with existing DRAM and SRAM architecture with relatively small associated cost added. STT-MRAM is essentially a magnetic multilayer resistive element cell that is fabricated as an additional metal layer on top of conventional CMOS access transistors. In this review we give an overview of the existing STT-MRAM technologies currently in research and development across the world, as well as some specific discussion of results obtained at Grandis and with our foundry partners. We will show that in-plane STT-MRAM technology, particularly the DMTJ design, is a mature technology that meets all conventional requirements for an STT-MRAM cell to be a nonvolatile solution matching DRAM and/or SRAM drive circuitry. Exciting recent developments in perpendicular STT-MRAM also indicate that this type of STT-MRAM technology may reach maturity faster than expected, allowing even smaller cell size and product introduction at smaller nodes.

390 citations

Journal ArticleDOI
TL;DR: In this paper, an island growth mode produces quantum dot regions in which the lateral confinement of excitons is directly revealed through the observation of resolution-limited (full width at half maximum of 0.8 meV) emission peaks in near-field photoluminescence spectra.
Abstract: Control of the growth dynamics during the epitaxy of coherently strained ZnSe/CdSe quantum structures results in a varied interfacial texture that broadly defines two qualitatively different regimes for exciton localization. An island growth mode produces quantum dot regions in which the lateral confinement of excitons is directly revealed through the observation of resolution-limited (full width at half maximum of 0.8 meV) emission peaks in near-field photoluminescence spectra. By contrast, layer-by-layer growth produces potential fluctuations at length scales small compared to the exciton diameter, so that the localization of excitons is driven by a random interfacial potential with a smooth density of states.

152 citations


Cited by
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Journal ArticleDOI
TL;DR: This work directly confirms the DW chirality and rigidity by examining current-driven DW dynamics with magnetic fields applied perpendicular and parallel to the spin spiral and resolves the origin of controversial experimental results.
Abstract: In most ferromagnets the magnetization rotates from one domain to the next with no preferred handedness. However, broken inversion symmetry can lift the chiral degeneracy, leading to topologically rich spin textures such as spin spirals and skyrmions through the Dzyaloshinskii-Moriya interaction (DMI). Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy metal and an oxide, the DMI stabilizes chiral domain walls (DWs) whose spin texture enables extremely efficient current-driven motion. We show that spin torque from the spin Hall effect drives DWs in opposite directions in Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a Neel configuration with left-handed chirality. We directly confirm the DW chirality and rigidity by examining current-driven DW dynamics with magnetic fields applied perpendicular and parallel to the spin spiral. This work resolves the origin of controversial experimental results and highlights a new path towards interfacial design of spintronic devices.

1,591 citations

Journal ArticleDOI
TL;DR: It is demonstrated by numerical investigations that an isolated skyrmion can be a stable configuration in a nanostructure, can be locally nucleated by injection of spin-polarized current, and can be displaced by current-induced spin torques, even in the presence of large defects.
Abstract: Magnetic skyrmions are topologically stable spin configurations, which usually originate from chiral interactions known as Dzyaloshinskii-Moriya interactions. Skyrmion lattices were initially observed in bulk non-centrosymmetric crystals, but have more recently been noted in ultrathin films, where their existence is explained by interfacial Dzyaloshinskii-Moriya interactions induced by the proximity to an adjacent layer with strong spin-orbit coupling. Skyrmions are promising candidates as information carriers for future information-processing devices due to their small size (down to a few nanometres) and to the very small current densities needed to displace skyrmion lattices. However, any practical application will probably require the creation, manipulation and detection of isolated skyrmions in magnetic thin-film nanostructures. Here, we demonstrate by numerical investigations that an isolated skyrmion can be a stable configuration in a nanostructure, can be locally nucleated by injection of spin-polarized current, and can be displaced by current-induced spin torques, even in the presence of large defects.

1,520 citations

Journal ArticleDOI
TL;DR: A review of the underlying physics of the stabilization of skyrmions at room temperature and their prospective use for spintronic applications is discussed in this paper, where the development of topological spintronics holds promise for applications in the mid-term furure, even though many challenges such as the achievement of writing, processing and reading functionalities at room-temperature and in all-electrical manipulation schemes, still lie ahead.
Abstract: Magnetic skyrmions are small swirling topological defects in the magnetization texture. Their stabilization and dynamics depend strongly on their topological properties. In most cases, they are induced by chiral interactions between atomic spins in non-centrosymmetric magnetic compounds or in thin films with broken inversion symmetry. Skyrmions can be extremely small, with diameters in the nanometre range, and behave as particles that can be moved, created and annihilated, which makes them suitable for ‘abacus’-type applications in information storage and logic technologies. Until recently, skyrmions had been observed only at low temperature and, in most cases, under large applied magnetic fields. An intense research effort has led to the identification of thin-film and multilayer structures in which skyrmions are now stable at room temperature and can be manipulated by electrical currents. The development of skyrmion-based topological spintronics holds promise for applications in the mid-term furure, even though many challenges, such as the achievement of writing, processing and reading functionalities at room temperature and in all-electrical manipulation schemes, still lie ahead. Magnetic skyrmions are topologically protected spin whirls that hold promise for applications because they can be controllably moved, created and annihilated. In this Review, the underlying physics of the stabilization of skyrmions at room temperature and their prospective use for spintronic applications are discussed.

1,462 citations

Journal ArticleDOI
TL;DR: An internal effective magnetic field arises from a Dzyaloshinskii-Moriya interaction at the Co/Pt interfaces and, in concert with spin Hall currents, drives the domain walls in lock-step along the nanowire.
Abstract: Spin-polarized currents provide a powerful means of manipulating the magnetization of nanodevices, and give rise to spin transfer torques that can drive magnetic domain walls along nanowires. In ultrathin magnetic wires, domain walls are found to move in the opposite direction to that expected from bulk spin transfer torques, and also at much higher speeds. Here we show that this is due to two intertwined phenomena, both derived from spin–orbit interactions. By measuring the influence of magnetic fields on current-driven domain-wall motion in perpendicularly magnetized Co/Ni/Co trilayers, we find an internal effective magnetic field acting on each domain wall, the direction of which alternates between successive domain walls. This chiral effective field arises from a Dzyaloshinskii–Moriya interaction at the Co/Pt interfaces and, in concert with spin Hall currents, drives the domain walls in lock-step along the nanowire. Elucidating the mechanism for the manipulation of domain walls in ultrathin magnetic films will enable the development of new families of spintronic devices. The influence of magnetic fields on the current-driven motion of domain walls in nanowires with perpendicular anisotropy shows that two spin–orbit-derived mechanisms are responsible for their motion.

1,114 citations

Journal ArticleDOI
TL;DR: In this article, the authors focus on the recent advances on the route to devices prototypes, focusing on thin film and multilayered structures in which skyrmions are stabilized above room temperature and manipulated by current.
Abstract: Magnetic skyrmions are small swirling topological defects in the magnetization texture stabilized by the protection due to their topology. In most cases they are induced by chiral interactions between atomic spins existing in non-centrosymmetric magnetic compounds or in thin films in which inversion symmetry is broken by the presence of an interface. The skyrmions can be extremely small with diameters in the nanometer range and, importantly, they behave as particles that can be moved, created or annihilated, making them suitable for abacus-type applications in information storage, logic or neuro-inspired technologies. Up to the last years skyrmions were observed only at low temperature (and in most cases under large applied fields) but important efforts of research has been recently devoted to find thin film and multilayered structures in which skyrmions are stabilized above room temperature and manipulated by current. This article focuses on these recent advances on the route to devices prototypes.

1,023 citations