Indirect exchange coupling between magnetic adatoms in carbon nanotubes

Costa, A. T.; Kirwan, D. F.; Ferreira, M. S.

doi:10.1103/physrevb.72.085402

Cited by 52 publications

(77 citation statements)

References 14 publications

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“…A monotonic form is found for the black line representing V g = 0, due to the familiar commensurability effect that exists in half-filled electronic bands in hexagonal atomic structures. [27][28][29][30] As a matter of fact, for the same reason, this monotonicity is also found everywhere outside the gated region. As the gate voltage is increased to V g = ⌬ and V g =2⌬ we depart from a commensurate regime and enter a region where clear oscillatory patterns are seen.…”

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confidence: 91%

Graphene-based spin-pumping transistor

et al. 2010

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We demonstrate with a fully quantum-mechanical approach that graphene can function as gate-controllable transistors for pumped spin currents, i.e., a stream of angular momentum induced by the precession of adjacent magnetizations, which exists in the absence of net charge currents. Furthermore, we propose as a proof of concept how these spin currents can be modulated by an electrostatic gate. Because our proposal involves nanosized systems that function with very high speeds and in the absence of any applied bias, it is potentially useful for the development of transistors capable of combining large processing speeds, enhanced integration, and extremely low-power consumption. DOI: 10.1103/PhysRevB.81.233402 PACS number͑s͒: 72.25.Pn, 85.75.Ϫd, 81.05.ue, 72.80.Vp The field of spintronics, responsible for a number of exciting proposals for future electronic devices, is based on ingenious ways of controlling not only how the electron current flows across magnetic ͑M͒ and nonmagnetic ͑NM͒ hybrid materials, but also how the electron spin propagates throughout this environment.1 One of the most sought-after applications in the field is the generation of efficient spin transistors capable of modulating the transport properties, depending on the spin of the current-carrying electrons.2 Such a spin-polarized current has been produced in several instances, detected in a variety of ways 3 and has as a common characteristic the fact that the scattering contrast that exists between M and NM regions in these hybrid materials leads to the sought transistor behavior.Current challenges for producing spin transistors are in designing structures in which: ͑i͒ the spin coherence length is larger than or at least comparable with the system size; ͑ii͒ spin-polarized currents can be efficiently injected from the M to the NM regions of the system. Here, we argue that graphene has the ideal properties to overcome both limitations and propose that it can be used as a spin transistor that allows control of spin transport through an electrostatic gate. Furthermore, our proposal involves nanoscaled systems that function with very high speeds and in the absence of any applied bias, which can in principle pave the way toward the construction of transistors combining increasingly large data processing speeds, enhanced integration and extremely lowelectric power consumption.The first bottleneck is likely to be overcome with the use of graphene if we recall numerous predictions that have been made for extremely long spin-coherence lengths for these materials 4-7 when compared to conventional metallic structures. In fact, recent experimental evidences confirming these predictions have also indicated how much room there is for increasing this length. 8 The second obstacle arises primarily due to the inherent contact resistance that exists between the M and NM regions. It has a spin-independent part, commonly referred to as background resistance, added to a contribution that depends on the electron spin. Depending on the value of this background...

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Graphene-based spin-pumping transistor

et al. 2010

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“…Earlier calculations have suggested that the existence of this current is sufficient to induce a dynamic magnetic coupling between dispersed impurities in NT, which is far more pronounced and long ranged than any other magnetic coupling of static nature. 7,8,14,15 To test how this precession propagates, in Fig. 2 we show ͉͗S m ͑t͉͒͘ probed at different locations on the NT.…”

Section: ͑1͒mentioning

confidence: 99%

“…For a pristine NT g mj ͑ ͒ may be analytically determined 14 and the integration in Eq. ͑1͒ performed with great numerical accuracy.…”

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confidence: 99%

Carbon nanotube: A low-loss spin-current waveguide

et al. 2010

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We demonstrate with a quantum-mechanical approach that carbon nanotubes are excellent spin-current waveguides and are able to carry information stored in a precessing magnetic moment for long distances with very little dispersion and with tunable degrees of attenuation. Pulsed magnetic excitations are predicted to travel with the nanotube Fermi velocity and are able to induce similar excitations in remote locations. Such an efficient way of transporting magnetic information suggests that nanotubes are promising candidates for memory devices with fast magnetization switchings. DOI: 10.1103/PhysRevB.81.153408 PACS number͑s͒: 73.63.Fg, 72.25.Ba, 75.30.Hx, 75.75.Ϫc The issue of magnetization dynamics in low-dimensional systems is currently one of the most studied in spintronics. 1 In particular, controlling how quickly the energy of a precessing magnetic moment propagates through wires is motivated by the possibility of building miniaturized memory devices with fast magnetization switchings. This requires structures functioning as efficient spin-current waveguides, i.e., conduits capable of transporting spin information with little attenuation. Renowned for their high thermal and electronic conductivities, for their long aspect ratios and coherence lengths, carbon nanotubes ͑NT͒ possess the ideal characteristics for acting as waveguides. NT have indeed been shown to function as conduits for electrons 2,3 and for phonons. 4 A natural question to ask, raised in this Brief Report, is whether these materials are also efficient spin-current waveguides.Tserkovnyak 5,6 proposed a mechanism for pumping spin current into a nonmagnetic metal caused by the precession of an adjacent magnetization. In this case, angular momentum from the moving magnetization is transferred to the conduction electrons, creating a spin disturbance that propagates throughout the metallic conduit. This spin flow is produced without an applied voltage, involves no net electrical current, and may be used to excite other magnetic units also in contact with the nonmagnetic metal. Our strategy is to test this mechanism with NT in contact to local magnetic moments.Obstacles for identifying good spin waveguides lie in the difficulties of predicting the precise time evolution of the magnetization of a realistic system, taking into consideration the details of its electronic structure. This requires a full understanding of how a pulsed magnetic excitation evolves. Although previously treated semiclassically 5,6 and quantum mechanically, 7,8 a time-dependent quantum approach for this problem is still missing. In this Brief Report we bridge this gap and provide a quantum formalism that describes in time domain how a localized magnetic perturbation propagates throughout a nanoscale system, more precisely a metallic NT. In doing so, we are able to show that NT are excellent spin-current waveguides. We demonstrate that they transport spin current across long distances in a dispersionless fashion and with little attenuation. Moreover, we indicate that pulsed s...

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“…We will call the energies of the acoustic and optical mode as ⍀ 0 and ⍀ 1 , respectively. The existence of a frequency splitting between the two modes means that there is a static Ruderman-KittelKasuya-Yoshida ͑RKKY͒-type exchange coupling between m ជ A and m ជ B , 12 which is proportional to the splitting. The solid curve displays a measure of the dynamical coupling, −Im BA ͑⍀͒; its absolute value is proportional to the amplitude of the magnetization precession induced on B by a transverse circularly polarized field applied on A.…”

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confidence: 99%

“…The splitting is proportional to the static exchange coupling between m ជ A and m ជ B , which is known to oscillate as a function of N. [12][13][14] The static coupling decays, for quasi-one-dimensional systems, asymptotically as 1 / N; hence oscillations in the dynamic coupling should be seen even for relatively large values of N.…”

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confidence: 99%

Long-ranged dynamic magnetic interaction through low-dimensional systems

et al. 2008

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Magnetic units attached to low-dimensional metallic nanowires are known to interact via the conduction electrons of the wire leading to preferential alignment directions of the respective magnetic moments. In addition to this so-called static interaction, here we show that a very long-ranged interaction arises when these units are allowed to precess. This dynamic version of the magnetic interaction governs the spin dynamics of the magnetic moments. We are able to relate this interaction to the spin excitation spectrum of the system in which we establish a clear correspondence between the precession relaxation time and the features of the spin susceptibility. We show that the relaxation time is predominantly determined by the availability of noncoherent Stoner modes, a process analogous to Landau damping of plasmons in the electron gas. Contrary to expectations, our results indicate that the range of this interaction is robust against the introduction of disorder. Furthermore, we show that the interaction range is frequency dependent suggesting that it may be tunable by an adequate choice of excitation frequencies. We argue that this may pave the way to controlling the communication between distant parts of a spintronic device. Magnetic moments embedded in nonmagnetic metallic media interact with each other via the spin polarization induced in the latter. Due to its relevance from fundamental and applied viewpoints, this interaction has been thoroughly investigated during the last two decades 1 and has proven to play essential roles in recent scientific and technological developments. 2 Less well known are the dynamical aspects of that coupling: clearly, if one of the magnetizations is set in motion the others will also precess. If the dynamic interaction that produces such induced precession is sufficiently long ranged, this phenomenon may be exploited as a communication channel between distant parts of spintronic devices. When compared to the charge channel traditionally used in electronic devices, the spin channel has the advantage of being almost dissipationless for appropriate choices of materials. Schemes for synchronizing large sets of oscillators have also been devised based on the dynamic coupling between magnetic moments. 3,4 The dynamic coupling is intimately related to the spin current emitted by a magnetic volume whose magnetization has been driven out of equilibrium. 5 This same spin current is responsible for the enhanced Gilbert damping predicted and observed in a variety of metallic systems 6-8 and is also closely related to the system's spin excitation spectrum. The dynamic coupling has been investigated in the context of three-dimensional magnetic multilayers, within a semiclassical approach 9 and a full quantum theoretic analysis. 5 There, as it has been shown, 9 the range of the dynamic coupling is limited only by spin-orbit interaction. In that work, however, the frequency dependence of the dynamic coupling was not explored ͑the frequency of the driving field was assumed to satisfy the condi...

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Indirect exchange coupling between magnetic adatoms in carbon nanotubes

Cited by 52 publications

References 14 publications

Graphene-based spin-pumping transistor

Graphene-based spin-pumping transistor

Carbon nanotube: A low-loss spin-current waveguide

Long-ranged dynamic magnetic interaction through low-dimensional systems

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