Current-driven excitation of magnetic multilayers
IBM1
TL;DR: In this paper, a new mechanism was proposed for exciting the magnetic state of a ferromagnet, where a transfer of vectorial spin accompanied an electric current flowing perpendicular to two parallel magnetic films connected by a normal metallic spacer.
About: This article is published in Journal of Magnetism and Magnetic Materials.The article was published on 1996-06-01. It has received 5824 citations till now. The article focuses on the topics: Spin polarization & Spin Hall effect.
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TL;DR: This review describes a new paradigm of electronics based on the spin degree of freedom of the electron, which has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices.
Abstract: This review describes a new paradigm of electronics based on the spin degree of freedom of the electron. Either adding the spin degree of freedom to conventional charge-based electronic devices or using the spin alone has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices. To successfully incorporate spins into existing semiconductor technology, one has to resolve technical issues such as efficient injection, transport, control and manipulation, and detection of spin polarization as well as spin-polarized currents. Recent advances in new materials engineering hold the promise of realizing spintronic devices in the near future. We review the current state of the spin-based devices, efforts in new materials fabrication, issues in spin transport, and optical spin manipulation.
9,917 citations
TL;DR: Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems as discussed by the authors, where the primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport.
Abstract: Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.
9,158 citations
IBM1
TL;DR: The racetrack memory described in this review comprises an array of magnetic nanowires arranged horizontally or vertically on a silicon chip and is an example of the move toward innately three-dimensional microelectronic devices.
Abstract: Recent developments in the controlled movement of domain walls in magnetic nanowires by short pulses of spin-polarized current give promise of a nonvolatile memory device with the high performance and reliability of conventional solid-state memory but at the low cost of conventional magnetic disk drive storage. The racetrack memory described in this review comprises an array of magnetic nanowires arranged horizontally or vertically on a silicon chip. Individual spintronic reading and writing nanodevices are used to modify or read a train of ∼10 to 100 domain walls, which store a series of data bits in each nanowire. This racetrack memory is an example of the move toward innately three-dimensional microelectronic devices.
4,052 citations
TL;DR: In this paper, a giant spin Hall effect (SHE) in β-tantalum was shown to generate spin currents intense enough to induce spin-torque switching of ferromagnets at room temperature.
Abstract: Spin currents can apply useful torques in spintronic devices. The spin Hall effect has been proposed as a source of spin current, but its modest strength has limited its usefulness. We report a giant spin Hall effect (SHE) in β-tantalum that generates spin currents intense enough to induce efficient spin-torque switching of ferromagnets at room temperature. We quantify this SHE by three independent methods and demonstrate spin-torque switching of both out-of-plane and in-plane magnetized layers. We furthermore implement a three-terminal device that uses current passing through a tantalum-ferromagnet bilayer to switch a nanomagnet, with a magnetic tunnel junction for read-out. This simple, reliable, and efficient design may eliminate the main obstacles to the development of magnetic memory and nonvolatile spin logic technologies.
3,330 citations
TL;DR: Inter interfacial perpendicular anisotropy between the ferromagnetic electrodes and the tunnel barrier of the MTJ is used by employing the material combination of CoFeB-MgO, a system widely adopted to produce a giant tunnel magnetoresistance ratio in MTJs with in-plane an isotropy.
Abstract: Magnetic tunnel junctions (MTJs) with ferromagnetic electrodes possessing a perpendicular magnetic easy axis are of great interest as they have a potential for realizing next-generation high-density non-volatile memory and logic chips with high thermal stability and low critical current for current-induced magnetization switching. To attain perpendicular anisotropy, a number of material systems have been explored as electrodes, which include rare-earth/transition-metal alloys, L1(0)-ordered (Co, Fe)-Pt alloys and Co/(Pd, Pt) multilayers. However, none of them so far satisfy high thermal stability at reduced dimension, low-current current-induced magnetization switching and high tunnel magnetoresistance ratio all at the same time. Here, we use interfacial perpendicular anisotropy between the ferromagnetic electrodes and the tunnel barrier of the MTJ by employing the material combination of CoFeB-MgO, a system widely adopted to produce a giant tunnel magnetoresistance ratio in MTJs with in-plane anisotropy. This approach requires no material other than those used in conventional in-plane-anisotropy MTJs. The perpendicular MTJs consisting of Ta/CoFeB/MgO/CoFeB/Ta show a high tunnel magnetoresistance ratio, over 120%, high thermal stability at dimension as low as 40 nm diameter and a low switching current of 49 microA.
3,169 citations
References
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IBM1
TL;DR: In this article, a theory is given for three closely related effects involving a nonmagnetic electron-tunneling barrier separating two ferromagnetic conductors, and the theory predicts that the valve effect is weak and that the coupling is antiferromagnetic (Jl0).
Abstract: A theory is given for three closely related effects involving a nonmagnetic electron-tunneling barrier separating two ferromagnetic conductors. The first is Julliere's magnetic valve effect, in which the tunnel conductance depends on the angle \ensuremath{\theta} between the moments of the two ferromagnets. One finds that discontinuous change of the potential at the electrode-barrier interface diminishes the spin-polarization factor governing this effect and is capable of changing its sign. The second is an effective interfacial exchange coupling -J cos\ensuremath{\theta} between the ferromagnets. One finds that the magnitude and sign of J depend on the height of the barrier and the Stoner splitting in the ferromagnets. The third is a new, irreversible exchange term in the coupled dynamics of the ferromagnets. For one sign of external voltage V, this term describes relaxation of the Landau-Lifshitz type. For the opposite sign of V, it describes a pumping action which can cause spontaneous growth of magnetic oscillations. All of these effects were investigated consistently by analyzing the transmission of charge and spin currents flowing through a rectangular barrier separating free-electron metals. In application to Fe-C-Fe junctions, the theory predicts that the valve effect is weak and that the coupling is antiferromagnetic (Jl0). Relations connecting the three effects suggest experiments involving small spatial dimensions.
1,455 citations
TL;DR: Measurements at 4.2 K of the magnetoresistance (MR) measured with the current perpendicular to the layer planes (CPP) of equal and unequal thickness Ag/Co magnetic multilayers that display giant MR measured withThe current in the layerplanes (CIP) are presented.
Abstract: We present measurements at 4.2 K of the magnetoresistance (MR) measured with the current perpendicular to the layer planes (CPP) of equal and unequal thickness Ag/Co magnetic multilayers that display giant MR measured with the current in the layer planes (CIP). For Ag layer thicknesses from 2 to 60 nm, and Co thicknesses from 6 to 15 nm, the CPP MR extends up to nearly 50% and ranges from 3 times to more than 10 times as large as the CIP MR for the same samples
539 citations
TL;DR: A close analogy between oscillations in the exchange coupling and de Haas-van Alphen oscillations is established and exploited to show that the period, asymptotic decay, and temperature dependence of the oscillations are determined by properties of the Fermi surface in the spacer layer.
Abstract: A theory of oscillations in the exchange coupling between two transition-metal ferromagnets separated by a nonmagnetic transition-metal spacer is developed for a one-band model. A close analogy between oscillations in the exchange and de Haas--van Alphen oscillations is established and exploited to show that the period, asymptotic decay, and temperature dependence of the oscillations are determined by properties of the Fermi surface in the spacer layer. The theory describes many features of the oscillations in the exchange coupling observed recently in Co/Ru, Co/Cr, and Fe/Cr superlattices.
336 citations
TL;DR: To test this and related models, the extremal spanning vectors and the associated Fermi-surface geometrical factors have been calculated for a large set of spacer-layer materials and interface orientations.
Abstract: Many structures consisting of magnetic layers separated by a nonmagnetic spacer layer show an oscillatory exchange coupling. This behavior is explained in terms of a simple model that shows that the Fermi surface of the spacer-layer material is responsible for the oscillatory coupling. The periods of the oscillatory coupling are set by extremal spanning vectors of the Fermi surface of the spacer-layer material. The strength of the coupling depends both on the geometry of the Fermi surface and on the reflection amplitudes for electrons scattering from the interfaces between the spacer layers and the magnetic layers. To test this and related models, the extremal spanning vectors and the associated Fermi-surface geometrical factors have been calculated for a large set of spacer-layer materials and interface orientations. These models are at least consistent with the experimental data. All measured oscillation periods are consistent with the calculated periods, but particularly for transition metals there are many more periods calculated than are seen experimentally.
273 citations
IBM1
TL;DR: In this article, basic mechanisms of interlayer exchange coupling between two ferromagnets separated by a non-magnetic spacer are surveyed, and three special mechanisms of non-cos θ coupling are described: fluctuations of spacer thickness, loose spins, and a novel phenomenological coupling through a nonnormal spacer.
246 citations