Giant Spin Hall: One of the primary challenges in the field of spin-electronics, which exploits the electron's spin rather than its charge, is to create strong currents of electrons with polarized spins. One way to do this is to use a ferromagnet as a polarizer, a principle used in magnetic tunnel junctions; however, these devices suffer from reliability problems. An alternative is the spin Hall effect, where running a charge current through a material generates a spin current in the transverse direction, but the efficiency of this process tends to be small. Liu et al. (p. 555 ) now show that the spin Hall effect in Tantalum in its high-resistance β phase generates spin currents strong enough to induce switching of the magnetization of an adjacent ferromagnet; at the same time, Ta does not cause energy dissipation in the ferromagnet. These properties allowed efficient and reliable operation of a prototype three-terminal device.

We report a giant spin Hall effect (SHE) in {\beta}-W thin films. Using spin torque induced ferromagnetic resonance with a {\beta}-W/CoFeB bilayer microstrip we determine the spin Hall angle to be |\theta|=0.30\pm0.02, large enough for an in-plane current to efficiently reverse the orientation of an in-plane magnetized CoFeB free layer of a nanoscale magnetic tunnel junction adjacent to a thin {\beta}-W layer. From switching data obtained with such 3-terminal devices we independently determine |\theta|=0.33\pm0.06. We also report variation of the spin Hall switching efficiency with W layers of different resistivities and hence of variable ({\alpha} and {\beta}) phase composition

We report that spin current transport across Pt/ferromagnet (FM) interfaces as measured by the spin torques exerted on the FM is strongly dependent on the type and the thickness of the FM layer and on post-deposition processing protocols. By employing both harmonic voltage measurements and spin-torque ferromagnetic resonance measurements, we find that the efficiency of the Pt spin Hall effect in exerting a dampinglike spin torque on the FM corresponds to an effective spin Hall ratio ranging from $<0.05$ to $>0.10$ under different interfacial conditions. The “internal” spin Hall ratio of the Pt thin films used in this study, after taking the interfacial spin transmission factor into account, is estimated to be $\sim 0.30$. This suggests that a careful engineering of $\mathrm{Pt}/\mathrm{FM}$ interfaces can improve the spin Hall torque efficiency of Pt-based spintronic devices. We also note that the dependence on temperature for both vector components of the spin Hall torque is strongly dependent on the details of the $\mathrm{Pt}/\mathrm{FM}$ interface, and that measurements of magnetic damping as a function of FM layer thickness are not generally reliable for determining the true effective spin mixing conductance for the interface.

We report that by measuring a current-induced hysteresis loop shift versus in-plane bias magnetic field, the spin-Hall effect (SHE) contribution of the current-induced effective field per current density ${\chi }_{\mathrm{SHE}}$ can be estimated for Pt- and Ta-based magnetic heterostructures with perpendicular magnetic anisotropy. We apply this technique to a Pt-based sample with its ferromagnetic (FM) layer being wedged deposited and discover an extra effective field contribution ${\chi }_{\mathrm{Wedged}}$ due to the asymmetric nature of the deposited FM layer. We confirm the correlation between ${\chi }_{\mathrm{Wedged}}$ and the asymmetric depinning process in FM layer during magnetization switching by magneto-optical Kerr microscopy. These results indicate the possibility of engineering deterministic spin-orbit torque switching by controlling the symmetry of domain expansion through the materials growth process.

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.