Spin currents can apply useful torques in spintronic devices. The spin Hall effect has been proposed as a source of spin current, but its modest strength has limited its usefulness. We report a giant spin Hall effect (SHE) in β-tantalum that generates spin currents intense enough to induce efficient spin-torque switching of ferromagnets at room temperature. We quantify this SHE by three independent methods and demonstrate spin-torque switching of both out-of-plane and in-plane magnetized layers. We furthermore implement a three-terminal device that uses current passing through a tantalum-ferromagnet bilayer to switch a nanomagnet, with a magnetic tunnel junction for read-out. This simple, reliable, and efficient design may eliminate the main obstacles to the development of magnetic memory and nonvolatile spin logic technologies.

We demonstrate that the spin Hall effect in a thin film with strong spin-orbit scattering can excite magnetic precession in an adjacent ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer generates an oscillating transverse spin current in the Pt, and the resultant transfer of spin angular momentum to the NiFe induces ferromagnetic resonance (FMR) dynamics. The Oersted field from the current also generates an FMR signal but with a different symmetry. The ratio of these two signals allows a quantitative determination of the spin current and the spin Hall angle. We study Pt/Permalloy bilayer films with a microwave-frequency (RF) charge current applied in the film plane (Permalloy = Py = Ni 81 Fe 19 ). An oscillating transverse spin current is generated in the Pt by the SHE and injected into the adjacent Py ( Fig. 1(a)), thereby exerting an oscillating spin torque (ST) on the Py that induces magnetization precession. This leads to an oscillation of the bilayer resistance due to the anisotropic magnetoresistance (AMR) of Py. A DC voltage signal is generated across the sample from the mixing of the RF current and the oscillating resistance, similar to the signal that arises from ST induced FMR in spin valves and magnetic tunnel junctions [12][13][14][15]. The resonance properties enable a quantitative measure of the spin current absorbed by the Py.Our measurement setup is shown in Fig. 1(c). Pt/Py bilayers were grown by DC magnetron sputter deposition. The starting material for the Pt was 99.95% pure. Highly resistive 3 Ta (1 nm) was employed as the capping layer to prevent oxidation of the Py. The bilayers were subsequently patterned into microstrips of 1 to 20 μm wide and 3 to 250 μm long. By using a bias tee, we were able to apply a microwave current and at the same time measure the DC voltage. A sweeping magnetic field H ext was applied in the film plane, with the angle θ between H ext and microstrip kept at 45° unless otherwise indicated. The output power of the microwave signal generator was varied from 0 to 20 dBm and the measured DC voltage was proportional to the applied power, indicating that the induced precession was in the small angle regime. All the measurements we present were performed at room temperature with a power of 10 dBm.We model the motion of the Py magnetic moment m by the Landau-Lifshitz-GilbertHere γ is the gyromagnetic ratio, α is the Gilbert damping coefficient, μ 0 is the permeability in vacuum, M s is the saturation magnetization of Py, t is the thickness of the Py layer, , / 2 S RF J erepresents the oscillating spin current density injected into Py, H RF is the Oersted field generated by the RF current, H eff is the sum of H ext and the demagnetization field 4π M eff , and σ is the direction of the injected spin moment. The third and fourth terms on the right hand side of Eq. (1) are the result of in-plane spin torque and the out-of-plane torque due to the Oersted field, respectively ( Fig. 1(a)). The mixing signal in response to a combination of in...

We show that in a perpendicularly magnetized Pt/Co bilayer the spin-Hall effect (SHE) in Pt can produce a spin torque strong enough to efficiently rotate and switch the Co magnetization. We calculate the phase diagram of switching driven by this torque, finding quantitative agreement with experiments. When optimized, the SHE torque can enable memory and logic devices with similar critical currents and improved reliability compared to conventional spin-torque switching. We suggest that the SHE torque also affects current-driven magnetic domain wall motion in Pt/ferromagnet bilayers.

In the spin Hall effect (SHE) 1-3 the application of a charge current through a nonmagnetic material results in the generation of a transverse spin current due to the spin-orbit interaction.This transverse spin current can be described by2e is the spin current density, e J the charge current density ,  the spin polarization unit vector and / SH s e J J   is the material-dependent spin Hall angle. Previous studies have demonstrated that the magnitudes of the spin Hall angles in the 5d elements Pt 4-9 and high resistivity β-Ta 10 can be relatively large, Pt SH   0.07 and -Ta

We show that a direct current in a tantalum microstrip can induce steady-state magnetic oscillations in an adjacent nanomagnet through spin torque from the spin Hall effect (SHE). The oscillations are detected electrically via a magnetic tunnel junction (MTJ) contacting the nanomagnet. The oscillation frequency can be controlled using the MTJ bias to tune the magnetic anisotropy. In this 3-terminal device, the SHE torque and the MTJ bias therefore provide independent controls of the oscillation amplitude and frequency, enabling new approaches for developing tunable spin torque nano-oscillators.