Spin-to-charge conversion is an essential requirement for the implementation of spintronic devices. Recently, monolayers of semiconducting transition metal dichalcogenides (TMDs) have attracted considerable interest for spin-to-charge conversion due to their high spin-orbit coupling and lack of inversion symmetry in their crystal structure. However, reports of direct measurement of spin-to-charge conversion at TMD-based interfaces are very much limited. Here, we report on the room temperature observation of a large spin-to-charge conversion arising from the interface of Ni80Fe20 (Py) and four distinct large area (∼ 5 × 2 mm 2 ) monolayer (ML) TMDs namely, MoS2, MoSe2, WS2, and WSe2. We show that both spin mixing conductance and the Rashba efficiency parameter (λIREE) scales with the spin-orbit coupling strength of the ML TMD layers. The λIREE parameter is found to range between −0.54 and −0.76 nm for the four monolayer TMDs, demonstrating a large spin-tocharge conversion. Our findings reveal that TMD/ferromagnet interface can be used for efficient generation and detection of spin current, opening new opportunities for novel spintronic devices.

Nanomagnetic and spintronic devices, which make use of physical phenomena in materials and interfaces like perpendicular magnetic anisotropy (PMA) and spin–orbit torque (SOT) to exhibit multiple electrically readable and controllable states, have been widely considered as synaptic elements in analog crossbar arrays for on-chip learning of analog neural networks (ANN). Here, in such a heavy-metal-ferromagnetic-metal-oxide-heterostructure-based (Pt/Co/SiO2) spintronic device, multiple mixed states are first demonstrated experimentally. These mixed states correspond to different magnetization configurations between two saturated states: all magnetic moments vertically up and all moments vertically down (the ferromagnetic layer exhibits PMA). These mixed states are then modulated through in-plane-current pulses, which result in SOT at the heavy-metal–ferromagnet interface, and thus long-term potentiation (LTP) and long-term depression (LTD) are demonstrated in the device (synaptic behavior). The experimentally obtained LTP-and-LTD behavior is explained qualitatively through micromagnetic simulations, which model the interface phenomena phenomenologically. The synaptic bit resolution is then determined experimentally to be 5 (≈ 30 distinguishable states) by measuring the stability of the mixed states. The nonlinearity and asymmetry in the obtained LTP and LTD are quantified experimentally. Next, a crossbar-array-based ANN is simulated using spintronic-synapse-device models based on the experimentally obtained LTP and LTD, and reasonably high classification accuracy is predicted for MNIST and Fashion-MNIST data sets, despite the synaptic nonidealities like nonlinearity, asymmetry, and cycle-to-cycle variations. The impact of nonlinearity and asymmetry on classification accuracy is found to be much higher than that due to limited bit resolution (we do not go below 10 bits per synapse cell though) and cycle-to-cycle variations.

Spin pumping has been considered a powerful tool to manipulate the spin current in a ferromagnetic/nonmagnetic (FM/NM) system, where the NM part exhibits large spin–orbit coupling (SOC). In this work, the spin pumping in β-W/Interlayer (IL)/Co2FeAl (CFA) heterostructures grown on Si­(100) is systematically investigated with different ILs in which SOC strength ranges from weak to strong. We first measure the spin pumping through the enhancement of effective damping in CFA by varying the thickness of β-W. The damping enhancement in the bilayer of β-W/CFA (without IL) is found to be ∼50% larger than the Gilbert damping in a single CFA layer with a spin diffusion length and spin mixing conductance of 2.12 ± 0.27 nm and 13.17 ± 0.34 nm–2, respectively. Further, the ILs of different SOC strengths such as Al, Mg, Mo, and Ta were inserted at the β-W/CFA interface to probe their impact on damping in β-W/ILs/CFA. The effective damping reduced to 8% and 20% for Al and Mg, respectively, whereas it increased to 66% and 75% with ILs of Mo and Ta, respectively, compared to the β-W/CFA heterostructure. Thus, in the presence of ILs with weak SOC, the spin pumping at the β-W/CFA interface is suppressed, while for the high SOC ILs effective damping increased significantly from its original value of β-W/CFA bilayer using a thin IL. This is further confirmed by performing inverse spin Hall effect measurements. In summary, the transfer of spin angular momentum can be significantly enhanced by choosing a proper ultrathin interface layer. Our study provides a tool to increase the spin current production by inserting an appropriate thin interlayer which is useful in modifying the heterostructure for efficient performance in spintronics devices.

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