Through combined ferromagnetic resonance, spin pumping, and inverse spin Hall effect experiments in Co|Pt bilayers and Co|Cu|Pt trilayers, we demonstrate consistent values of ℓsfPt=3.4±0.4 nm and ...θSHEPt=0.056±0.010 for the respective spin diffusion length and spin Hall angle for Pt. Our data and model emphasize the partial depolarization of the spin current at each interface due to spin-memory loss. Our model reconciles the previously published spin Hall angle values and explains the different scaling lengths for the ferromagnetic damping and the spin Hall effect induced voltage.
The spin-orbit interaction couples the electrons' motion to their spin. As a result, a charge current running through a material with strong spin-orbit coupling generates a transverse spin current ...(spin Hall effect, SHE) and vice versa (inverse spin Hall effect, ISHE). The emergence of SHE and ISHE as charge-to-spin interconversion mechanisms offers a variety of novel spintronic functionalities and devices, some of which do not require any ferromagnetic material. However, the interconversion efficiency of SHE and ISHE (spin Hall angle) is a bulk property that rarely exceeds ten percent, and does not take advantage of interfacial and low-dimensional effects otherwise ubiquitous in spintronic hetero- and mesostructures. Here, we make use of an interface-driven spin-orbit coupling mechanism-the Rashba effect-in the oxide two-dimensional electron system (2DES) LaAlO
/SrTiO
to achieve spin-to-charge conversion with unprecedented efficiency. Through spin pumping, we inject a spin current from a NiFe film into the oxide 2DES and detect the resulting charge current, which can be strongly modulated by a gate voltage. We discuss the amplitude of the effect and its gate dependence on the basis of the electronic structure of the 2DES and highlight the importance of a long scattering time to achieve efficient spin-to-charge interconversion.
The Rashba effect is an interaction between the spin and the momentum of electrons induced by the spin-orbit coupling (SOC) in surface or interface states. Its potential for conversion between charge ...and spin currents has been theoretically predicted but never clearly demonstrated for surfaces or interfaces of metals. Here we present experiments evidencing a large spin-charge conversion by the Bi/Ag Rashba interface. We use spin pumping to inject a spin current from a NiFe layer into a Bi/Ag bilayer and we detect the resulting charge current. As the charge signal is much smaller (negligible) with only Bi (only Ag), the spin-to-charge conversion can be unambiguously ascribed to the Rashba coupling at the Bi/Ag interface. This result demonstrates that the Rashba effect at interfaces can be used for efficient charge-spin conversion in spintronics.
Torques appear between charge carrier spins and local moments in regions of ferromagnetic media where spatial magnetization gradients occur, such as a domain wall, owing to an exchange interaction. ...This phenomenon has been predicted by different theories and confirmed in a number of experiments on metallic and semiconductor ferromagnets. Understanding the magnitude and orientation of such spin-torques is an important problem for spin-dependent transport and current-driven magnetization dynamics, as domain-wall motion underlies a number of emerging spintronic technologies. One outstanding issue concerns the non-adiabatic spin-torque component β, which has an important role in wall dynamics, but no clear consensus has yet emerged over its origin or magnitude. Here, we report an experimental measurement of β in perpendicularly magnetized films with narrow domain walls (1-10 nm). By studying thermally activated wall depinning, we deduce β from the variation of the Arrhenius transition rate with applied currents. Surprisingly, we find β to be small and relatively insensitive to the wall width, which stands in contrast to predictions from transport theories. In addition, we find β to be close to the Gilbert damping constant α, which, in light of similar results on planar anisotropy systems, suggests a universal origin for the non-adiabatic torque.
We report the observation of spin-to-charge current conversion in strained mercury telluride at room temperature, using spin pumping experiments. We show that a HgCdTe barrier can be used to protect ...the HgTe from direct contact with the ferromagnet, leading to very high conversion rates, with inverse Edelstein lengths up to 2.0±0.5 nm. The influence of the HgTe layer thickness on the conversion efficiency is found to differ strongly from what is expected in spin Hall effect systems. These measurements, associated with the temperature dependence of the resistivity, suggest that these high conversion rates are due to the spin momentum locking property of HgTe surface states.
We present the analysis of the spin signals obtained in NiFe based metallic lateral spin valves. We exploit the spin-dependent diffusive equations in both the conventional one-dimensional (1D) ...analytic modeling and in 3D finite element method simulations. These approaches are used for extracting the spin diffusion length and the effective spin polarization in Py/Al, Py/Cu, and Py/Au based lateral nanostructures at both 300 K and 77 K. Both the analytic modeling and 3D finite element method simulations give consistent results. The combination of these models provides a powerful tool for reliable spin transport characterization in all metallic spin valves and gives an insight into the spin/charge current and spin accumulations 3D distributions in these devices. We provide the necessary ingredients to develop the 3D finite element modeling of diffusive spin transport.
The spin-orbit coupling relating the electron spin and momentum allows for spin generation, detection and manipulation. It thus fulfils the three basic functions of the spin field-effect transistor. ...However, the spin Hall effect in bulk germanium is too weak to produce spin currents, whereas large Rashba effect at Ge(111) surfaces covered with heavy metals could generate spin-polarized currents. The Rashba spin splitting can actually be as large as hundreds of meV. Here we show a giant spin-to-charge conversion in metallic states at the Fe/Ge(111) interface due to the Rashba coupling. We generate very large charge currents by direct spin pumping into the interface states from 20 K to room temperature. The presence of these metallic states at the Fe/Ge(111) interface is demonstrated by first-principles electronic structure calculations. By this, we demonstrate how to take advantage of the spin-orbit coupling for the development of the spin field-effect transistor.
We present measurements of pure spin current absorption on lateral spin valves. By varying the width of the absorber we demonstrate that spin current absorption measurements enable one to ...characterize efficiently the spin transport properties of ferromagnetic elements. The analytical model used to describe the measurement takes into account the polarization of the absorber. The analysis of the measurements thus allows the determination of the polarization and the spin diffusion length of a studied material independently, contrary to most experiments based on lateral spin valves where those values are entangled. We report the spin transport parameters of some of the most important materials used in spinorbitronics (Co60Fe40, Ni81Fe19, Co, Pt, and Ta), at room and low (10 K) temperatures.
The spin absorption process in a ferromagnetic material depends on the spin orientation relative to the magnetization. Using a ferromagnet to absorb the pure spin current created within a lateral ...spin valve, we evidence and quantify a sizable orientation dependence of the spin absorption in Co, CoFe, and NiFe. These experiments allow us to determine the spin-mixing conductance, an elusive but fundamental parameter of the spin-dependent transport. We show that the obtained values cannot be understood within a model considering only the Larmor, transverse decoherence, and spin diffusion lengths, and rather suggest that the spin-mixing conductance is actually limited by the Sharvin conductance.
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