We report that spin current transport across Pt-ferromagnet (FM) interfaces 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 damping-like spin torque on the FM ranges from < 0.05 to > 0.10 under different interfacial conditions. We also show that the temperature dependence of the spin torque efficiencies for both the dampinglike torque and field-like torque is dependent upon the details of the Pt-FM interface. The "internal" spin Hall angle of the Pt thin films used in this study, after taking the interfacial spin transmission factor into account, is estimated to be ~ 0.20. This suggests that a careful engineering of Pt-FM interfaces can improve the spin-Hall-torque efficiency of Pt-based spintronic devices. The spin Hall effect (SHE) [1, 2] causes an electrical current density e J flowing through a material with strong spin-orbit interactions to generate a transverse spin current density s J . The amplitude of s J is characterized by the spin Hall angle . The most straightforward way to determine a lower bound [3], θ SH LB , on the spin Hall angle in normal metal (NM) systems is to measure the current-dependent torque that is exerted on an adjacent ferromagnet (FM) when spin current flows to the NM-FM interface. Research has shown [4, 5]that there are two different components of torque that can be observed in this case: a "dampinglike" torque , where m is the orientation of the ferromagnetic moment, and a "field-like" torque . The determination via τ DL measurements of a large θ SH LB ≈ 0.07, in Pt-FM thin film bilayers [3, 6, 7], and the subsequent observation of even larger, "giant" spin Hall angles for high resistivity Ta (amorphous or β phase Ta), θ SH LB ≈ 0.12 [8] and β-W, θ SH LB ≈ 0.33 [9, 10], have opened up a very active area for research and technology development.Recent calculations utilizing Boltzmann analysis [11] and the drift-diffusion approximation [12] have noted that if the NM-FM interface is not completely transparent to the flow of the spin current then spin backflow will reduce the torque applied to the FM by the SHE.This reduction can be characterized, as suggested above, by defining a damping-like spin torque efficiency ξ DL , and also a field-like torque efficiency ξ FL , for a particular NM-FM interface, such that ξ DL can be less than or equal to the "internal" spin Hall angle θ SH that quantifies the spin current generated in the absence of an adjacent FM. Within a diffusive model, the effects of spin backflow are expected to modify the spin torque efficiencies in the form [11,12]

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We report that strong perpendicular magnetic anisotropy of the ferromagnetic layer in a W/CoFeB/MgO multilayer structure can be established by inserting a Hf layer as thin as 0.25 nm between the W and CoFeB layers. The Hf spacer also allows transmission of spin currents generated by an in-plane charge current in the W layer to apply strong spin torque on the CoFeB, thereby enabling current-driven magnetic switching. The antidamping-like and field-like components of the spin torque exerted on a 1 nm CoFeB layer are of comparable magnitudes in this geometry. Both components originate from the spin Hall effect in the underlying W layer.

The use of graphene in spintronic devices depends, among other things, on its ability to convert a spin excitation into an electric charge signal, a phenomenon that requires a spin-orbit coupling (SOC). Here we report the observation of two effects that show the existence of SOC in large-area CVD grown single-layer graphene deposited on a single crystal film of the ferrimagnetic insulator yttrium iron garnet (YIG). The first is a magnetoresistance of graphene induced by the magnetic proximity effect with YIG. The second is the detection of a dc voltage along the graphene layer resulting from the conversion of the spin current generated by spin pumping from microwave driven ferromagnetic resonance into a charge current, which is attributed to the inverse Rashba-Edelstein effect.

Direct current voltage appears across and in plane of a ferromagnetic multilayer experiencing ferromagnetic resonance. We have investigated the dc voltage simultaneously generated with the excitation of the uniform mode of magnetization precession in ferromagnetic∕normal-metal∕ferromagnetic trilayers with different spacer-layer materials. The generated voltage strongly depends on the chemical nature and the thickness of the normal-metal spacer as well as on the microwave incident power. This dc voltage might be correlated with the spin-pumping effect recently predicted.