Direct electronic measurement of the spin Hall effect

Abstract

The generation, manipulation and detection of spin-polarized electrons in nanostructures define the main challenges of spin-based electronics 1 . Amongst the different approaches for spin generation and manipulation, spin-orbit coupling, which couples the spin of an electron to its momentum, is attracting considerable interest. In a spin-orbit-coupled system a nonzero spincurrent is predicted in a direction perpendicular to the applied electric field, giving rise to a "spin Hall effect" 2,3,4 . Consistent with this effect, electrically-induced spin polarization was recently detected by optical techniques at the edges of a semiconductor channel 5 and in two-dimensional electron gases in semiconductor heterostructures 6,7 . Here we report electrical measurements of the spin-Hall effect in a diffusive metallic conductor, using a ferromagnetic electrode in combination with a tunnel barrier to inject a spin-polarized current. In our devices, we observe an induced voltage that results exclusively from the conversion of the injected spin current into charge imbalance through the spin Hall effect. Such a voltage is proportional to the component of the injected spins that is perpendicular to the plane defined by the spin current direction and the voltage probes. These experiments reveal opportunities for efficient spin detection without the need for magnetic materials, which could lead to useful spintronics devices that integrate information processing and data storage.The spin Hall effect (SHE), which was first described by Dyakonov and Perel 2,3 and more recently by Hirsch 4 , was proposed to occur in paramagnetic materials as a consequence of the spin-orbit interaction. In analogy to the standard Hall effect, the SHE refers to the generation of a pure spin current transverse to an applied electric field that results in an accompanying spin imbalance in the system. These early theoretical studies considered an extrinsic 2,3,4,8 SHE originating from an asymmetric scattering for spin-up and spin-down electrons. It was pointed out that, after scattering off an impurity, there is a spin-dependent probability difference in the electron trajectories which generates the spin imbalance. In the recently introduced intrinsic 9,10 SHE, spin imbalance is expected to occur even in the absence of scattering as a result of the band structure.Several experimental schemes have been proposed to electrically detect the extrinsic SHE in metals 4,8,11,12 . However, these schemes are difficult to implement. Spinrelated phenomena such as anisotropic magnetoresistance (AMR) in ferromagnetic (FM) electrodes, spin dependent interface scattering, or standard and anomalous Hall effects could render the SHE signal unobservable. We use the measurement scheme in Fig. 1 to study the SHE isolated from such spurious phenomena.It is natural to expect that, if a charge-current induces a transverse spin-imbalance through the spin-

Terahertz spin current pulses controlled by magnetic heterostructures

“…The spin flow is probed in a contactless manner using the inverse spin Hall effect 14,15 (ISHE) that converts the spin current into a detectable THz electromagnetic pulse 13 . Our findings open up a route to device-oriented femtosecond spintronics as well as novel broadband emitters of THz radiation 7,8,9 .…”

“…11,12,20). In order to probe j s , we borrow concepts from measurement schemes of static spin currents that take advantage of the ISHE 14,15 . As indicated in Fig.…”

“…1c). Whereas in static experiments the resulting charge current is measured as a voltage 14,15,24 , we here electrooptically sample the field of the electromagnetic pulse that is emitted by the charge current burst j c (see Fig. 1a and Methods).…”

Modulation of pure spin currents with a ferromagnetic insulator

“…This concept is the basis of new spindependent phenomena, including spin pumping [6][7][8][9][10][11][12], spin Seebeck effect [6,13], and spin Hall magnetoresistance (SMR) [6,[14][15][16][17][18]. In these cases, a NM with large spin-orbit coupling is required to convert the involved spin currents into charge currents via the inverse spin Hall effect [19].…”

Study of spin pumping in Co thin film vis-à-vis seed and capping layers using ferromagnetic resonance spectroscopy

“…A fundamental understanding of the exchange interaction and spin-orbital interaction at the interfaces will increase speed, energy efficiency, miniaturization of size and its multi-functional utilization [8]. Pure spin current is produced by asymmetric scattering of the two electrons with opposite spin angular momentum in the presence of spin orbit coupling at the interface which is known as spin Hall effect [1,3,9,10]. This is usually investigated via ferromagnetic resonance (FMR) in which a microwave excites the spin in ferromagnetic (FM) layers.…”