The Experts below are selected from a list of 1896 Experts worldwide ranked by ideXlab platform
Laurens W. Molenkamp - One of the best experts on this subject based on the ideXlab platform.
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Elementary Magnetoelectronics
IEEE Potentials, 2002Co-Authors: Gerrit E. W. Bauer, Georg Schmidt, Laurens W. MolenkampAbstract:The so-called giant magnetoresistance (GMR) effect is one of the few discoveries of basic physics and materials science that has netted industrial applications in as little as one decade. "Magnetoelectronics" is the technology that takes advantage of the additional functionality of metallic ferromagnets in electronic circuits and devices by employing the principles of the GMR and its derivates. The more catchy term of "spintronics" is often used to include, for example, single spin manipulations in nonmagnetic systems such as semiconductor quantum dots. This is often done with an eye on applications for "quantum computing." These and other exotic phenomena, such as macroscopic quantum coherence of magnetism, are outside the scope of this article. Here we will focus on the basic concepts of GMR-type of Magnetoelectronics with ferromagnets.
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Injection and detection of a spin-polarized current in a light-emitting diode
Nature, 1999Co-Authors: R. Flederling, Michael Kelm, G. Reuscher, W. Ossau, Andreas Waag, G Schmidt, Laurens W. MolenkampAbstract:The field of Magnetoelectronics has been growing in practical importance in recent years(1). For example, devices that harness electronic spin-such as giant-magnetoresistive sensors and magnetoresistive memory cells-are now appearing on the market(2). In contrast, magnetoelectronic devices based on spin-polarized transport in semiconductors are at a much earlier stage of development, largely because of the lack of an efficient means of injecting spin-polarized charge. Much work has focused on the use of ferromagnetic metallic contacts(3,4), but it has proved exceedingly difficult to demonstrate polarized spin injection. More recently, two groups(5,6) have reported successful spin injection from an NiFe contact, but the observed effects of the spin-polarized transport were quite small (resistance changes of less than 1%). Here we describe a different approach, in which the magnetic semiconductor BexMnyZn1-x-ySe is used as a spin aligner. We achieve injection efficiencies of 90% spin-polarized current into a nonmagnetic semiconductor device. The device used in this case is a GaAs/AlGaAs light-emitting diode, and spin polarization is confirmed by the circular polarization state of the emitted light.
Gerrit E. W. Bauer - One of the best experts on this subject based on the ideXlab platform.
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Noise and dissipation in magnetoelectronic nanostructures
Physical Review B, 2009Co-Authors: Jørn Foros, Gerrit E. W. Bauer, Arne Brataas, Yaroslav TserkovnyakAbstract:The interplay between current and magnetization fluctuations and dissipation in layered-ferromagnetic-normal-metal nanostructures is investigated. We use scattering theory and magnetoelectronic circuit theory to calculate charge and spin-current fluctuations. Via the spin-transfer torque, spin-current noise causes a significant enhancement of magnetization fluctuations. A special focus is on spin valves in which one of the ferromagnets is pinned. We find that the magnetization noise and damping are tensors that depend on the magnetic configuration. For symmetric spin valves in which both layers fluctuate, dynamic cross-talk between the layers becomes important, causing a possibly large difference in noise level between the parallel and antiparallel magnetic configurations. Due to giant magnetoresistance (GMR), the magnetization fluctuations in spin valves induce resistance noise, which is identified as a prominent source of electric noise at relatively high current densities. The resistance noise is shown to vary considerably with the magnetic configuration, partly due to the dependence of the angular GMR. The contribution from spin-current fluctuations to the resistance noise is shown to be significant. Resistance noise is an experimentally accessible quantity that can be measured to verify our results.
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Thermal spin-transfer torque in magnetoelectronic devices
Physical Review Letters, 2007Co-Authors: Moosa Hatami, Gerrit E. W. Bauer, Qinfang Zhang, Paul J. KellyAbstract:We predict that the magnetization direction of a ferromagnet can be reversed by the spin-transfer torque accompanying spin-polarized thermoelectric heat currents. We illustrate the concept by applying a finite-element theory of thermoelectric transport in disordered magnetoelectronic circuits and devices to metallic spin valves. When thermalization is not complete, a spin heat accumulation vector is found in the normal-metal spacer, i.e., a directional imbalance in the temperature of majority and minority spins.
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Non-collinear Magnetoelectronics
Physics Reports, 2006Co-Authors: Arne Brataas, Gerrit E. W. Bauer, Paul J. KellyAbstract:The electron transport properties of hybrid ferromagnetic|normal metal structures such as multilayers and spin valves depend on the relative orientation of the magnetization direction of the ferromagnetic elements. Whereas the contrast in the resistance for parallel and antiparallel magnetizations, the so-called giant magnetoresistance, is relatively well understood for quite some time, a coherent picture for non-collinear magnetoelectronic circuits and devices has evolved only recently. We review here such a theory for electron charge and spin transport with general magnetization directions that is based on the semiclassical concept of a vector spin accumulation. In conjunction with first-principles calculations of scattering matrices many phenomena, e.g. the current-induced spin-transfer torque, can be understood and predicted quantitatively for different material combinations.
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Magnetization noise in magnetoelectronic nanostructures
Physical Review Letters, 2005Co-Authors: Jørn Foros, Arne Brataas, Yaroslav Tserkovnyak, Gerrit E. W. BauerAbstract:By scattering theory we show that spin current noise in normal electric conductors in contact with nanoscale ferromagnets increases the magnetization noise by means of a fluctuating spin-transfer torque. Johnson-Nyquist noise in the spin current is related to the increased Gilbert damping due to spin pumping, in accordance with the fluctuation-dissipation theorem. Spin current shot noise in the presence of an applied bias is the dominant contribution to the magnetization noise at low temperatures.
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Magnetoelectronic spin echo.
Physical Review Letters, 2003Co-Authors: Arne Brataas, Yaroslav Tserkovnyak, Gergely Zaránd, Gerrit E. W. BauerAbstract:We predict a spin echo in electron transport through layered ferromagnetic-normal-ferromagnetic metal structures: whereas a spin current polarized perpendicular to the magnetization direction decays when traversing a single homogeneous ferromagnet on the scale of the ferromagnetic spin-coherence length, it partially reappears by adding a second identical but antiparallel ferromagnet. This reentrant transverse spin current resembles the spin-echo effect in the magnetization of nuclei under pulsed excitations. We propose an experimental setup to measure the spin echo.
Min-fa Lin - One of the best experts on this subject based on the ideXlab platform.
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Hofstadter spectra for d-orbital electrons: A case study on MoS2
RSC Advances, 2015Co-Authors: Min-fa LinAbstract:To study the Hofstadter spectrum of monolayer molybdenum disulfide (MoS2), we systematically examine the magnetic energy spectra due to various hoppings between d-orbital electrons to illustrate the link between the Bloch bands and the corresponding magnetoelectronic spectra. The magnetoelectronic spectrum shows a mirror (inversion) symmetry as a result of the particle–hole symmetry (asymmetry) in the Bloch bands. At small field, specific Landau fan diagrams can be ascribed to certain Bloch-band singularities. In the spectrum of real MoS2, we further find a breaking of spectral symmetry, the spin and valley polarization, and a flux-dependent energy gap. Our numerical results can facilitate a qualitative understanding of the topological nature of d-bands and provide a basis for exploring the Landau levels in transition-metal dichalcogenides.
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Magnetoelectronic properties of bilayer Bernal graphene
Physical Review B, 2008Co-Authors: Y. H. Lai, Cheng-peng Chang, Min-fa LinAbstract:The Peierls Hamiltonian band matrix is developed to investigate magnetoelectronic properties of bilayer Bernal graphene. A uniform perpendicular magnetic field creates many dispersionless Landau levels LLs at low and high energies and some oscillatory LLs at moderate energy. State degeneracy of the low LLs is two times as much as that of the high LLs. Wave functions and state energies are dominated by the interlayer atomic interactions and field strength B0. The former induce two groups of LLs, more low LLs, the asymmetric energy spectrum about the Fermi level, and the change of level spacing. Two sets of effective quantum numbers, n 1 ’s and n 2 ’s, are required to characterize all the wave functions. They are determined by the strongest oscillation modes of the dominant carrier densities; furthermore, they rely on the specific interlayer atomic hoppings. The dependence of the quite low Landau-level energies on B0 and n 1 is approximately linear. An energy gap is produced by the magnetic field and interlayer atomic hoppings. Eg grows with increasing field strength, while it is reduced by the Zeeman effect. The main features of magnetoelectronic structures are directly reflected in the density of states. The predicted electronic properties could be verified by the experimental measurements on absorption spectra and transport properties.
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Magnetoelectronic properties of a carbon nanotube pair
Diamond and Related Materials, 2008Co-Authors: Jiun Yi Lien, Min-fa LinAbstract:Electronic properties of a pair of single-walled carbon nanotubes under a uniform magnetic field are investigated by the tight-binding model. The low-energy band structures are mainly affected by the intertube interactions, the field strength, and the field direction (the azimuthal angle and the polar angle). The intertube interactions, which are closely related to the geometric structures, could destroy double degeneracy, hybridize the atomic wave functions between tubes, and thus create new subbands. Subband curvature, state degeneracy, and energy gaps are dominated by the nanotube radius and stacking types. The magnetic field would further modify energy dispersion, alter subband spacing, and induce semiconductor-metal transitions. Electronic properties are directly reflected in the density of states (DOS). DOS exhibits prominent asymmetric peaks due to the parabolic bands. The number, the heights, and the positions of the pronounced peaks are very sensitive to the intertube interactions and the magnetic field.
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Magnetoelectronic properties of finite double-walled carbon nanotubes
Physica E: Low-dimensional Systems and Nanostructures, 2008Co-Authors: C. H. Lee, R. B. Chen, Min-fa LinAbstract:Abstract Magnetoelectronic properties of finite double-walled carbon nanotubes, whose structure belongs to D 5 h , are studied by the tight-binding model. Energy levels, energy gaps, and density of states strongly depend on intertube hoppings, nanotube length, strength and direction of the magnetic field, and the Zeeman splitting. Intertube interactions could change level spacings, modify energy gaps, and destroy state symmetry about the chemical potential. Magnetic field could induce destruction of state degeneracy, increase of low-energy states, and strong modulation of energy gap. Moreover, the Zeeman splitting plays an important role in the above-mentioned magnetoelectronic properties.
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Magnetoelectronic Properties of a Single-Layer Graphite
Journal of the Physical Society of Japan, 2006Co-Authors: Y. H. Lai, Cheng-peng Chang, Sing-jyun Tsai, Jenn-shyong Hwang, Min-fa LinAbstract:The magnetoelectronic structure of a single-layer graphite is mainly determined by the strength, the period, and the direction of the modulated magnetic field. Such field could induce the destruction of state degeneracy, the drastic change of energy dispersion, the increment of band-edge states, and the alternation of band width. Most of energy bands become nondegenerate, and the flat bands are replaced by the parabolic bands. Density of states exhibits the linear energy dependence, the square-root divergences, the logarithmic divergences, the discontinuous structures, and the delta-function-like divergences. These special structures directly reflect rich energy spectra.
Arne Brataas - One of the best experts on this subject based on the ideXlab platform.
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Noise and dissipation in magnetoelectronic nanostructures
Physical Review B, 2009Co-Authors: Jørn Foros, Gerrit E. W. Bauer, Arne Brataas, Yaroslav TserkovnyakAbstract:The interplay between current and magnetization fluctuations and dissipation in layered-ferromagnetic-normal-metal nanostructures is investigated. We use scattering theory and magnetoelectronic circuit theory to calculate charge and spin-current fluctuations. Via the spin-transfer torque, spin-current noise causes a significant enhancement of magnetization fluctuations. A special focus is on spin valves in which one of the ferromagnets is pinned. We find that the magnetization noise and damping are tensors that depend on the magnetic configuration. For symmetric spin valves in which both layers fluctuate, dynamic cross-talk between the layers becomes important, causing a possibly large difference in noise level between the parallel and antiparallel magnetic configurations. Due to giant magnetoresistance (GMR), the magnetization fluctuations in spin valves induce resistance noise, which is identified as a prominent source of electric noise at relatively high current densities. The resistance noise is shown to vary considerably with the magnetic configuration, partly due to the dependence of the angular GMR. The contribution from spin-current fluctuations to the resistance noise is shown to be significant. Resistance noise is an experimentally accessible quantity that can be measured to verify our results.
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Non-collinear Magnetoelectronics
Physics Reports, 2006Co-Authors: Arne Brataas, Gerrit E. W. Bauer, Paul J. KellyAbstract:The electron transport properties of hybrid ferromagnetic|normal metal structures such as multilayers and spin valves depend on the relative orientation of the magnetization direction of the ferromagnetic elements. Whereas the contrast in the resistance for parallel and antiparallel magnetizations, the so-called giant magnetoresistance, is relatively well understood for quite some time, a coherent picture for non-collinear magnetoelectronic circuits and devices has evolved only recently. We review here such a theory for electron charge and spin transport with general magnetization directions that is based on the semiclassical concept of a vector spin accumulation. In conjunction with first-principles calculations of scattering matrices many phenomena, e.g. the current-induced spin-transfer torque, can be understood and predicted quantitatively for different material combinations.
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Magnetization noise in magnetoelectronic nanostructures
Physical Review Letters, 2005Co-Authors: Jørn Foros, Arne Brataas, Yaroslav Tserkovnyak, Gerrit E. W. BauerAbstract:By scattering theory we show that spin current noise in normal electric conductors in contact with nanoscale ferromagnets increases the magnetization noise by means of a fluctuating spin-transfer torque. Johnson-Nyquist noise in the spin current is related to the increased Gilbert damping due to spin pumping, in accordance with the fluctuation-dissipation theorem. Spin current shot noise in the presence of an applied bias is the dominant contribution to the magnetization noise at low temperatures.
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Magnetoelectronic spin echo.
Physical Review Letters, 2003Co-Authors: Arne Brataas, Yaroslav Tserkovnyak, Gergely Zaránd, Gerrit E. W. BauerAbstract:We predict a spin echo in electron transport through layered ferromagnetic-normal-ferromagnetic metal structures: whereas a spin current polarized perpendicular to the magnetization direction decays when traversing a single homogeneous ferromagnet on the scale of the ferromagnetic spin-coherence length, it partially reappears by adding a second identical but antiparallel ferromagnet. This reentrant transverse spin current resembles the spin-echo effect in the magnetization of nuclei under pulsed excitations. We propose an experimental setup to measure the spin echo.
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From Digital to Analogue Magnetoelectronics: Theory of Transport in Non-collinear Magnetic Nanostructures
Advances in Solid State Physics, 2003Co-Authors: Gerrit E. W. Bauer, Yaroslav Tserkovnyak, Daniel Huertas-hernando, Arne BrataasAbstract:Magnetoelectronics is mainly digital, i.e. governed by up and down magnetizations. In contrast, analogue Magnetoelectronics makes use of phenomena occuring for non-collinear magnetization configurations. Here we review theories which have recently been applied to the transport in non-collinear magnetic nanostructures in two and multiterminal structures, viz. random matrix and circuit theory. Both are not valid for highly transparent systems in a resistive environment like perpendicular metallic spin valves. The solution to this problem is a renormalization of the conventional and spin-mixing conductance parameters.
Oliver G. Schmidt - One of the best experts on this subject based on the ideXlab platform.
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Imperceptible Magnetoelectronics
Nature Communications, 2015Co-Authors: Michael Melzer, Martin Kaltenbrunner, Denys Makarov, Dmitriy Karnaushenko, Tsuyoshi Sekitani, Takao Someya, Oliver G. SchmidtAbstract:Birds and many other animals can sense the Earth’s magnetic field, but not human beings. Here, Melzer et al . develop a type of artificial skin based on giant magnetoresistive sensor foils with micrometre thickness, which can be stretched up to >250% without sacrifices in device performance. Future electronic skin aims to mimic nature’s original both in functionality and appearance. Although some of the multifaceted properties of human skin may remain exclusive to the biological system, electronics opens a unique path that leads beyond imitation and could equip us with unfamiliar senses. Here we demonstrate giant magnetoresistive sensor foils with high sensitivity, unmatched flexibility and mechanical endurance. They are
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Imperceptible Magnetoelectronics
Nature Communications, 2015Co-Authors: Michael Melzer, Martin Kaltenbrunner, Denys Makarov, Dmitriy Karnaushenko, Tsuyoshi Sekitani, Takao Someya, Oliver G. SchmidtAbstract:Future electronic skin aims to mimic nature’s original both in functionality and appearance. Although some of the multifaceted properties of human skin may remain exclusive to the biological system, electronics opens a unique path that leads beyond imitation and could equip us with unfamiliar senses. Here we demonstrate giant magnetoresistive sensor foils with high sensitivity, unmatched flexibility and mechanical endurance. They are 250% without sacrifices in device performance.
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Stretchable Magnetoelectronics.
Nano Letters, 2011Co-Authors: Michael Melzer, Denys Makarov, Alfredo Calvimontes, Daniil Karnaushenko, Stefan Baunack, Rainer Kaltofen, Yongfeng Mei, Oliver G. SchmidtAbstract:We fabricated [Co/Cu] multilayers revealing a giant magnetoresistance (GMR) effect on free-standing elastic poly(dimethylsiloxane) (PDMS) membranes. The GMR performance of [Co/Cu] multilayers on rigid silicon and on free-standing PDMS is similar and does not change with tensile deformations up to 4.5%. Mechanical deformations imposed on the sensor are totally reversible, due to the elasticity of the PDMS membranes. This remarkable performance upon stretching relies on a wrinkling of GMR layers on top of the PDMS membrane.