Spin currents in metallic nanostructures: Explicit calculations

Guimarães, Filipe S. M.; Costa, A. T.; Muniz, R. B.; Mills, D. L.

doi:10.1103/physrevb.84.054403

Cited by 8 publications

(7 citation statements)

References 44 publications

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“…Finally, we would like to investigate ways of extending the interaction range, since a long-ranged, strong interaction is paramount for device applications. One well known way of extending the range of the interaction between magnetic moments is to set one of the moments to precess [59,60]. Indeed, theoretical studies in graphene have already predicted a large increase in the interaction range in this situation [31].…”

Section: Discussionmentioning

confidence: 99%

Variable range of the RKKY interaction in edged graphene

Duffy

Gorman

Power

et al. 2013

J. Phys.: Condens. Matter

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Abstract. The indirect exchange interaction is one of the key factors in determining the overall alignment of magnetic impurities embedded in metallic host materials. In this work we examine the range of this interaction in magnetically-doped graphene systems in the presence of armchair edges using a combination of analytical and numerical Green function (GF) approaches. We consider both a semi-infinite sheet of graphene with a single armchair edge, and also quasi-one-dimensional armchair edged graphene nanoribbons (GNRs). While we find signals of the bulk decay rate in semi-infinite graphene and signals of the expected one-dimensional decay rate in GNRs, we also find an unusually rapid decay for certain instances in both, which manifests itself whenever the impurities are located at sites which are a multiple of three atoms from the edge. This decay behavior emerges from both the analytic and numerical calculations, and the result for semi-infinite graphene can be interpreted as an intermediate case between ribbon and bulk systems.Variable range of the RKKY interaction in edged graphene 2

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Section: Discussionmentioning

confidence: 99%

Variable range of the RKKY interaction in edged graphene

Duffy

Gorman

Power

et al. 2013

J. Phys.: Condens. Matter

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“…Recently magnetization reversal by the SHE induced spin transfer torque has been demonstrated [11,12]. The generation of a voltage by a spin current injected into a paramagnetic metal, the inverse spin Hall effect (ISHE), can be employed to detect the spin current due to spin pumping [13][14][15] by an adjacent ferromagnet under ferromagnetic resonance (FMR) conditions [8,16]. The ISHE has also been essential for the discovery of the spin Seebeck effect [17].…”

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confidence: 99%

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confidence: 99%

“…1 can be interpreted as a spin battery [26]. When the ferromagnetic film is thicker than its transverse spin-coherence length (a few monolayers), the adiabatically pumped spin current reads [13][14][15]26] where m is the unit vector of the magnetization direction and g "# is the (dimensionless) complex spin mixing conductance [27]. The pumping spin current creates a spin accumulation in N that induces a diffusion backflow of spins into F:…”

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confidence: 99%

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Spin Backflow and ac Voltage Generation by Spin Pumping and the Inverse Spin Hall Effect

2013

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The spin current pumped by a precessing ferromagnet into an adjacent normal metal has a constant polarization component parallel to the precession axis and a rotating one normal to the magnetization. The former is now routinely detected as a dc voltage induced by the inverse spin Hall effect (ISHE). Here we compute ac ISHE voltages much larger than the dc signals for various material combinations and discuss optimal conditions to observe the effect. The backflow of spin is shown to be essential to distill parameters from measured ISHE voltages for both dc and ac configurations. DOI: 10.1103/PhysRevLett.110.217602 PACS numbers: 76.50.+g, 72.25.Mk, 73.40.Àc In magnetoelectronics the electronic spin degree of freedom creates new functionalities that lead to applications in information technologies such as sensors and memories [1]. Central to much excitement in this field is the spin Hall effect (SHE) [2][3][4][5], i.e., the spin current induced normal to an applied charge current in the presence of spin-orbit interaction, as discovered optically in semiconductors [6,7] and subsequently electrically in metals [8][9][10]. Recently magnetization reversal by the SHE induced spin transfer torque has been demonstrated [11,12]. The generation of a voltage by a spin current injected into a paramagnetic metal, the inverse spin Hall effect (ISHE), can be employed to detect the spin current due to spin pumping [13][14][15] by an adjacent ferromagnet under ferromagnetic resonance (FMR) conditions [8,16]. The ISHE has also been essential for the discovery of the spin Seebeck effect [17].In recent experiments, dc voltages induced by the ISHE have been measured in many material combinations, thereby giving access to crucial parameters such as the spin Hall angle [18][19][20] and the spin mixing conductance [21], the material parameter determining, e.g., the effectiveness of interface spin-transfer torques [14]. For example, the magnitude and sign of the spin Hall angle has been determined for Permalloy ðPyÞjN bilayers for different normal metals N [18,19]. An approximate scaling relation for the spin pumping by numerous ferromagnets (F) has been discovered by comparing different FjPt bilayers as a function of excitation power [21]. However, it is far from easy to derive quantitative information from ISHE experiments [22]. As reviewed by the Cornell Collaboration [23], several experimental pitfalls should be avoided. At FMR, the dc ISHE voltage is small, scaling quadratically with the cone angle of the precessing magnetization. An important correction is caused by the back diffusion (''backflow'') of injected spins to the interface, which effectively reduces the spin current injection [14] and generates voltages normal to the interface [24,25]. This backflow has often been neglected in interpreting spin-pumping experiments, assuming that Pt, the metal of choice, can be treated like a perfect spin sink.The spin current injected by FMR into a normal metal consists of a dc component along the z axis parallel to the effective fiel...

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“…This can be understood in terms of the spin currents emanating from precessing moments. In this case, angular momentum from the moving magnetization is transferred to the conduction electrons, creating a spin disturbance that propagates throughout the conducting material [25][26][27] . In the case of graphene, the particularly weak spin-orbit coupling of carbon drives this disturbance further afield, explaining why the range of the dynamic form of the RKKY interaction is so much more long ranged.…”

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Dynamic RKKY interaction between magnetic moments in graphene nanoribbons

et al. 2016

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Graphene has been identified as a promising material with numerous applications, particularly in spintronics. In this paper we investigate the peculiar features of spin excitations of magnetic units deposited on graphene nanoribbons and how they can couple through a dynamical interaction mediated by spin currents. We examine in detail the spin lifetimes and identify a pattern caused by vanishing density of states sites in pristine ribbons with armchair borders. Impurities located on these sites become practically invisible to the interaction, but can be made accessible by a gate voltage or doping. We also demonstrate that the coupling between impurities can be turned on or off using this characteristic, which may be used to control the transfer of information in transistor-like devices.One of the continuing challenges of the present day is to increase the ratio of computational speed to power consumption and cost. The field of spintronics attempts to tackle this problem by utilizing electron spin in solid state devices. In contrast to charge currents, spin currents are in principle transported with substantially less dissipation 1 , thus giving rise to a potentially efficient way of transporting information through nanoscale systems. Development of these ideas has been frustrated by the difficulty in establishing long range spin currents, as they tend to decay over moderately short distances 2 . These obstacles appear to be addressed by graphene and some of its allotropes, which possess extremely long range spin coherence lengths, owing to their weak spin-orbit and hyperfine interactions 3-6 .Because pristine graphene is non-magnetic, most studies of the magnetic response of graphene are done in samples with added magnetic dopants 7-24 . The overall behavior of magnetically-doped graphene is thus crucially dependent on how these dopants interact with each other. Graphene plays a key role in determining the nature and range of this interaction. This is because, at all but the closest ranges, the interaction between magnetic impurities is mediated by conduction electrons of the host material. When calculated using second order perturbation theory, this is called the RKKY interaction, although the moniker is often applied to the interaction as a whole. The interaction is generally related to the dimensionality of the system, but the unusual band structure of graphene means that it sports a shorter than normal range 10,11,13,16,17 , and as such, methods of lengthening the interaction are sought.Among the possible strategies to extend the range of the magnetic interaction between impurities, one that seems particularly viable is setting the impurities in precessional motion 25 . In fact, the RKKY interaction between localized magnetic moments embedded in graphene has been predicted to become more long ranged once the magnetic moments are taken out of equilibrium and set to precess through spin pumping 19 . This can be understood in terms of the spin currents emanating from precessing moments. In this case, angular mo...

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Spin currents in metallic nanostructures: Explicit calculations

Cited by 8 publications

References 44 publications

Variable range of the RKKY interaction in edged graphene

Variable range of the RKKY interaction in edged graphene

Spin Backflow and ac Voltage Generation by Spin Pumping and the Inverse Spin Hall Effect

Dynamic RKKY interaction between magnetic moments in graphene nanoribbons

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