We have measured the spin injection efficiency and spin lifetime in Co2FeSi/n-GaAs lateral nonlocal spin valves from 20 to 300 K. We observe large (∼40 µV) spin valve signals at room temperature and injector currents of 10 3 A/cm 2 , facilitated by fabricating spin valve separations smaller than the 1 µm spin diffusion length and applying a forward bias to the detector contact. The spin transport parameters are measured by comparing the injector-detector contact separation dependence of the spin valve signal with a numerical model accounting for spin drift and diffusion. The apparent suppression of the spin injection efficiency at the lowest temperatures reflects a breakdown of the ordinary drift-diffusion model in the regime of large spin accumulation. A theoretical calculation of the D'yakonov-Perel spin lifetime agrees well with the measured n-GaAs spin lifetime over the entire temperature range. arXiv:1610.03797v1 [cond-mat.mes-hall]
A distinguishing feature of spin accumulation in ferromagnet–semiconductor devices is its precession in a magnetic field. This is the basis for detection techniques such as the Hanle effect, but these approaches become ineffective as the spin lifetime in the semiconductor decreases. For this reason, no electrical Hanle measurement has been demonstrated in GaAs at room temperature. We show here that by forcing the magnetization in the ferromagnet to precess at resonance instead of relying only on the Larmor precession of the spin accumulation in the semiconductor, an electrically generated spin accumulation can be detected up to 300 K. The injection bias and temperature dependence of the measured spin signal agree with those obtained using traditional methods. We further show that this approach enables a measurement of short spin lifetimes (<100 ps), a regime that is not accessible in semiconductors using traditional Hanle techniques.
We observe a dc voltage peak at ferromagnetic resonance (FMR) in samples consisting of a single ferromagnetic (FM) layer grown epitaxially on the n−GaAs (001) surface.The FMR peak is detected as an interfacial voltage with a symmetric line shape and is present in samples based on various FM/n-GaAs hetrostructures, including Co 2 MnSi/n-GaAs, Co 2 FeSi/n-GaAs and Fe/n-GaAs. We show that the interface bias voltage dependence of the FMR signal is identical to that of the tunneling anisotropic magnetoresistance (TAMR) over most of the bias range. Furthermore, we show how the precessing magnetization yields a dc FMR signal through the TAMR effect and how the TAMR phenomenon can be used to predict the angular dependence of the FMR signal. This TAMR-induced FMR peak can be observed under conditions where no spin accumulation is present and no spin-polarized current flows in the semiconductor.
The hyperfine field from dynamically polarized nuclei in n-GaAs is very spatially inhomogeneous, as the nuclear polarization process is most efficient near the randomly-distributed donors. Electrons with polarized spins traversing the bulk semiconductor will experience this inhomogeneous hyperfine field as an effective fluctuating spin precession rate, and thus the spin polarization of an electron ensemble normal to the fluctuating hyperfine fields will relax. A theory of spin relaxation based on the theory of random walks is applied to such an ensemble precessing in an oblique magnetic field, and the precise form of the (unequal) longitudinal and transverse spin relaxation is analytically derived. To investigate this mechanism, electrical three-terminal Hanle measurements were performed on epitaxially grown Co 2 MnSi/n-GaAs heterostructures fabricated into electrical spin injection devices. The proposed anisotropic spin relaxation mechanism is required to satisfactorily describe the Hanle lineshapes when the applied field is oriented at large oblique angles.Introduction. -The understanding of electrical injection and detection of spin in ferromagnetic/semiconductor devices has progressed significantly over the past decade. 1,2 A key obstacle for interpreting spin transport experiments near the metal-insulator transition has been the complicating presence of dynamically polarized nuclear spins. [3][4][5] In the process of dynamic nuclear polarization (DNP), the electron spin polarization, maintained out of equilibrium optically or electrically, is transferred to the nuclear system over long time scales via the hyperfine interaction.6-10 The process can produce 99% polarized nuclei at room temperature in SiC and induce nuclear fields up to 5.3 T in GaAs. The nature and distribution of the electronic states controls the properties of the resulting effective hyperfine fields from DNP; for instance, electron spins in itinerant states interact rapidly with a multitude of nuclei, which dilutes the effect and leads to inefficient nuclear polarization. Spins situated at impurity sites, however, interact with many fewer nuclei, which promotes a more efficient 6 DNP. At the doping levels examined here, the different donor wave functions overlap often but do not completely fill the bulk crystal, which consequently results in a high degree of nuclear field inhomogeneity [see Figure 1]. 11,12 Previous descriptions of the spin transport dynamics in n-doped semiconductors with spin drift-diffusion equations 5,13-17 have neglected this essential inhomogeneity of the nuclear field.In the past, it has been sufficient to treat the nuclear polarization as a mean field and to assume only a single spin lifetime. This has been adequate to account for the magnitudes of the hyperfine fields, although there have always been discrepancies when quantitatively modeling Hanle effect experiments. It has been impossible to model lineshapes for different degrees of non-collinearity with a single spin lifetime. 5 Here we predict a new spin relax...
We report on an all-electrical measurement of the spin Hall effect in epitaxial Fe/In x Ga 1−x As heterostructures with n-type channel doping (Si) and highly doped Schottky tunnel barriers. A transverse spin current generated by an ordinary charge current flowing in the In x Ga 1−x As is detected by measuring the spin accumulation at the edges of the channel. The spin accumulation is identified through the observation of a Hanle effect in the Hall voltage measured by pairs of ferromagnetic contacts. We investigate the bias and temperature dependence of the resulting Hanle signal and determine the skew and side-jump contributions to the total spin Hall conductivity.
In the non-local spin valve (NLSV) geometry, four-terminal electrical Hanle effect measurements have the potential to provide a particularly simple determination of the lifetime ( ) and diffusion length ( ) of spins injected into non-magnetic materials. Recent work, however, has demonstrated that traditional models typically used to fit such data provide an inaccurate measurement of in ferromagnet/nonmagnetic metal (FM/N) devices with low interface resistance, particularly when the separation of the source and detector contacts is small. In the transparent limit, this shortcoming is due to the backdiffusion and subsequent relaxation of spins within the FM contacts, which is not properly accounted for in standard models of the Hanle effect. Here we have used the separation dependence of the spin accumulation signal in NLSVs with multiple FM/N combinations, and interfaces in the diffusive limit, to determine in traditional spin valve measurements. We then compare these results to Hanle measurements as analyzed using models that either include or exclude spin sinking. We demonstrate that differences between the spin valve and Hanle measurements of can be quantitatively modelled, provided that both the FM contact-induced isotropic spin-sinking and the full three-dimensional geometry of the devices, which is particularly important at small contact separations, are accounted for.We find, however, that considerable difficulties persist, in particular due to the sensitivity of fitting to the contact interface resistance and the FM contact magnetization rotation, in precisely determining with the Hanle technique alone, particularly at small contact separations. † Corresponding author: lao24@cam.ac.uk No's: 72.25.Ba, 72.25.Mk, 72.25.Rb PACS
We investigate the dynamically polarized nuclear-spin system in Fe/n-GaAs heterostructures using the response of the electron-spin system to nuclear magnetic resonance (NMR) in lateral spinvalve devices. The hyperfine interaction is known to act more strongly on donor-bound electron states than on those in the conduction band. We provide a quantitative model of the temperature dependence of the occupation of donor sites. With this model we calculate the ratios of the hyperfine and quadrupolar nuclear relaxation rates of each isotope. For all temperatures measured, quadrupolar relaxation limits the spatial extent of nuclear spin-polarization to within a Bohr radius of the donor sites and is directly responsible for the isotope dependence of the measured NMR signal amplitude. The hyperfine interaction is also responsible for the 2 kHz Knight shift of the nuclear resonance frequency that is measured as a function of the electron spin accumulation. The Knight shift is shown to provide a measurement of the electron spin-polarization that agrees qualitatively with standard spin transport measurements.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.