Tunneling anisotropic spin polarization in lateral (Ga,Mn)As/GaAs spin Esaki diode devices

Einwanger, Andreas; Ciorga, Mariusz; Wurstbauer, Ulrich; Schuh, Dieter; Wegscheider, Werner; Weiss, Dieter

doi:10.1063/1.3247187

Cited by 20 publications

(23 citation statements)

References 16 publications

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“…A difference is, however, observed, attributed to anisotropy of the tunneling process. [39][40][41] Apart from some quantitative differences, the results for GaAs-and Si-based devices are remarkably similar.…”

Section: Spin Precession In Gaas Near a Ferromagnetic Interfacesupporting

confidence: 51%

Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface

et al. 2011

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Although the creation of spin polarization in various nonmagnetic media via electrical spin injection from a ferromagnetic tunnel contact has been demonstrated, much of the basic behavior is heavily debated. It is reported here that, for semiconductor/Al 2 O 3 /ferromagnet tunnel structures based on Si or GaAs, local magnetostatic fields arising from interface roughness dramatically alter and even dominate the accumulation and dynamics of spins in the semiconductor. Spin precession in inhomogeneous magnetic fields is shown to reduce the spin accumulation up to tenfold, and causes it to be inhomogeneous and noncollinear with the injector magnetization. The inverted Hanle effect serves as the experimental signature. This interaction needs to be taken into account in the analysis of experimental data, particularly in extracting the spin lifetime τ s and its variation with different parameters (temperature, doping concentration). It produces a broadening of the standard Hanle curve and thereby an apparent reduction of τ s . For heavily doped n-type Si at room temperature it is shown that τ s is larger than previously determined, and a new lower bound of 0.29 ns is obtained. The results are expected to be general and to occur for spins near a magnetic interface not only in semiconductors but also in metals and organic and carbon-based materials including graphene, and in various spintronic device structures.

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Section: Spin Precession In Gaas Near a Ferromagnetic Interfacesupporting

confidence: 51%

Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface

et al. 2011

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“…12,13,20 An ASA may results from an anisotropic spin-relaxation time (τ s ) in the Si, from Hanle precession of spins in Si (due to the fact that the magnetization makes an angle θ with the external field) or due to tunneling anisotropic spin polarization. 2,22,23 …”

Section: B Measurement Techniquementioning

confidence: 99%

“…This leads to the change in resistance of the tunnel contact. Other sources of the anisotropy include the anisotropic tunnel spin polarization (TASP) associated with the ferromagnet/tunnel barrier interface 22,23 and/or anisotropic spin relaxation time τ s inside the nonmagnetic SC. Such an anisotropic spin relaxation has been invoked to describe experiments with graphene, 24 where it was argued that there is 20% decrease in spin-relaxation time for electrons with spin perpendicular to the graphene layer compared to the spins oriented parallel to the layer.…”

Section: Introductionmentioning

confidence: 99%

Anisotropy of spin polarization and spin accumulation in Si/Al2O3/ferromagnet tunnel devices

et al. 2012

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The contribution of the spin accumulation to tunneling anisotropy in Si/Al 2 O 3 /ferromagnet devices was investigated. Rotation of the magnetization of the ferromagnet from in-plane to perpendicular to the tunnel interface reveals a tunneling anisotropy that depends on the type of the ferromagnet (Fe or Ni) and on the doping of the Si (n or p type). Analysis shows that different contributions to the anisotropy coexist. Besides the regular tunneling anisotropic magnetoresistance, we identify a contribution due to anisotropy of the tunnel spin polarization of the oxide/ferromagnet interface. This causes the spin accumulation to be anisotropic, i.e., dependent on the absolute orientation of the magnetization of the ferromagnet.

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“…In this Letter we provide clear evidence of spin injection into a high mobility 2DEG confined in an inverted ðAl; GaÞAs=GaAs heterojunction, employing the ferromagnetic (FM) semiconductor (Ga,Mn)As in an Esaki diode configuration [18][19][20][21] as a spin aligner. We observed a dramatically enhanced nonlocal spin valve (NLSV) signal at negatively biased Esaki junctions when electrons can tunnel directly from (Ga,Mn)As into 2DEG states.…”

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confidence: 99%

Electrical Spin Injection into High Mobility 2D Systems

et al. 2014

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We report on spin injection into a high mobility 2D electron system confined at an ðAl; GaÞAs=GaAs interface, using (Ga,Mn)As Esaki diode contacts as spin aligners. We measured a clear nonlocal spin valve signal, which varies nonmonotonically with the applied bias voltage. The magnitude of the signal cannot be described by the standard spin drift-diffusion model, because at maximum this would require the spin polarization of the injected current to be much larger than 100%, which is unphysical. A strong correlation of the spin signal with contact width and electron mean free path suggests that ballistic transport in the 2D region below ferromagnetic contacts should be taken into account to fully describe the results. DOI: 10.1103/PhysRevLett.113.236602 PACS numbers: 72.25.Dc, 72.25.Hg, 72.25.Mk, 73.40.Kp All-electrical spin injection and detection, one of the key ingredients for functional spintronics devices, has been successfully realized in bulk semiconductors like GaAs [1,2] and Si [3,4]. To implement the spin-transistor functionality, proposed by Datta and Das [5], one needs the capacity to controllably rotate the spin of electrons on the way from source to drain. It has been suggested [5] to employ Rashba spin-orbit interaction, due to which the k vector of an electron in a two-dimensional electron gas (2DEG) is connected to an effective magnetic field, which is in turn tunable by an electric field. Thus, the precession angle in a sufficiently narrow channel can be coherently controlled by a gate voltage, provided transport between source and drain is ballistic. Hence, high mobility 2D systems are needed for these experiments. Although spin injection into graphene, a truly 2D system, has already been realized [6,7], no experiments exist in the ballistic regime where the injector or detector widths or their separation is significantly smaller than the electron mean free path l mf . Spin injection into semiconductor-based 2DEGs turns out to be difficult and only a few reports are available [8][9][10][11]. The analysis of experiments is also complicated by the lack of a corresponding ballistic theory. Although different aspects of ballistic spin injection and spin transport have been discussed theoretically [12][13][14][15][16][17], there is no comprehensive theory that would allow us to describe the experimental outcome in this regime in a way in which the spin drift-diffusion theory describes experiments on devices with bulk 3D channels [1,2].In this Letter we provide clear evidence of spin injection into a high mobility 2DEG confined in an inverted ðAl; GaÞAs=GaAs heterojunction, employing the ferromagnetic (FM) semiconductor (Ga,Mn)As in an Esaki diode configuration [18-21] as a spin aligner. We observed a dramatically enhanced nonlocal spin valve (NLSV) signal at negatively biased Esaki junctions when electrons can tunnel directly from (Ga,Mn)As into 2DEG states. At maximum the amplitude of the signal is much larger than predicted by the standard spin drift-diffusion model. The signal is especially l...

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Tunneling anisotropic spin polarization in lateral (Ga,Mn)As/GaAs spin Esaki diode devices

Cited by 20 publications

References 16 publications

Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface

Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface

Anisotropy of spin polarization and spin accumulation in Si/Al2O3/ferromagnet tunnel devices

Electrical Spin Injection into High Mobility 2D Systems

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