Spin pumping in nanolayers of WS2/Co2FeAl heterostructures: Large spin mixing conductance and spin transparency

Abstract

Materials with high spin–orbit coupling (SOC) are a prerequisite for the realization of spin–orbit torque-based magnetic memories. Transition metal dichalcogenides (TMDs) are an apt choice for such applications due to their high SOC strength. In this work, we have investigated the spin pumping phenomenon at the interface between thin tungsten disulphide (WS2) films and Co2FeAl (CFA) Heusler alloy films by performing ferromagnetic resonance (FMR) measurements on WS2/CFA heterostructures capped with the 4 nm thin Al film. While Raman spectroscopy conclusively proves the number of monolayers in the WS2 films, atomic force microscopy and x-ray reflectivity measurements were used to quantify the smoothness of the grown interfaces (<0.4 nm) as well as the individual layer thicknesses in the heterostructure stacks. Here, we vary the WS2 layer numbers and CFA thicknesses to quantify the spin pumping parameters such as spin mixing conductance, and spin transparency. FMR measurements revealed that damping enhancement reached ∼41% with a monolayer of WS2. Interfacial effective spin mixing conductance and spin transparency of the WS2/CFA interface are found to be 7.47 ± 0.97 nm−2 and 73.35 ± 9.52%, respectively. Thus, high-quality TMDs can be used as efficient materials for magnetic memory device applications.

High temperature stability in few atomic layer MoS2 based thin film heterostructures: structural, static and dynamic magnetization properties

“…However, the nearly same enhancement in the Δ α eff and g ↑↓ eff values (w.r.t. single layer CoFeB) for the as-deposited and annealed series observed in the present case of MoS 2 /CoFeB heterostructures is remarkably similar to those reported in the literature for CoFeB/W, 2,11 Co 2 FeAl/MoS 2 , 15 NiFe/MoS 2 , 18 Co 2 FeAl/Mo, 43 CoFeB/Mo, 61 CoFeB/WS 2 , 62 Co 2 FeAl/WS 2 , 71 CoFeB/Sb 2 Te 3 , 85 and CoFeB/Ta 86,87 heterostructures. Hence, the bilayer combination of CoFeB and MoS 2 could also be another highly commendable and MoS 2 could be a strong candidate material for robust spin angular moment transfer-based applications.…”

“…This transfer of spin angular momentum through SOC in the NM layer (here MOS 2 ) causes an enhancement in α eff . 71 The variation in Δ α eff with n L revealed an almost similar enhancement in damping i.e. , ∼49% and 51% for TMD2 and TMD2A series samples compared to that in the single CoFeB layer (as deposited and annealed).…”

“…However, for spin angular momentum to relax via this SOC, it needs to pass through at least one ML thick MoS 2 . 15,71 Consequently, there is a flow of spin angular momentum through ML thick MoS 2 layer, as seen in Fig. 5(f ).…”

“…Along with the spin pumping efficiency parameters related to spin relaxation, another important static parameter is the surface anisotropy energy-density ( K s ), which is related to the PMA. 71 Fig. 6(a) shows the f versus μ 0 H r plots of CoFeB(8 nm), MoS 2 (ML)/CoFeB(4 nm), and MoS 2 (ML)/CoFeB(15 nm) heterostructures.…”

Automated mechanical exfoliation technique: a spin pumping study in YIG/TMD heterostructures

“…Comparing TMDs coupled to conductor ferromagnetic layers (Py, Co, CoFeB, CoFeAl), like Py/TMD, for instance, the g ↑↓ values reported by other groups 47,85–88 are close to the ones shown in Table 1. However, due to the extremely low YIG's Gilbert damping, j s is orders of magnitude higher.…”