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Enhancement of spin Hall angle by an order of magnitude via Cu intercalation in MoS$_2$/CoFeB heterostructures

Abhisek Mishra, Pritam Das, Rupalipriyadarsini Chhatoi, Soubhagya Dash, Shubhransu Sahoo, Kshitij Singh Rathore, Pil-Ryung Cha, Seung-Cheol Lee, Satadeep Bhattacharjee, Subhankar Bedanta

TL;DR

The paper demonstrates that inserting a Cu spacer between MoS2 and CoFeB dramatically enhances spin-to-charge conversion by decoupling MoS2 from FM proximity effects, preserving its SOC. FMR-ISHE measurements reveal a spin Hall angle up to $\theta_{SHA}=0.30$ at $t_{Cu}=5$ nm, about an order of magnitude higher than MoS$_2$/CoFeB bilayers. Complementary MOKE and SQUID analyses confirm decoupling and improved spin-transport characteristics, while DFT-Wannier90 calculations show increased spin Berry curvature, intrinsic SHC, and higher MAE for the Cu-containing stack, consistent with SOC preservation. The results highlight interface engineering with interlayers as a viable route to high-efficiency spintronic devices and may extend to other TMD/FM systems.

Abstract

Transition metal dichalcogenides (TMDs) are a novel class of quantum materials with significant potential in spintronics, optoelectronics, valleytronics, and opto-valleytronics. TMDs exhibit strong spin-orbit coupling, enabling efficient spin-charge interconversion, which makes them ideal candidates for spin-orbit torque-driven spintronic devices. In this study, we investigated the spin-to-charge conversion through ferromagnetic resonance in MoS$_2$/Cu/CoFeB heterostructures with varying Cu spacer thicknesses. The conversion efficiency, quantified by the spin Hall angle, was enhanced by an order of magnitude due to Cu intercalation. Magneto-optic Kerr effect microscopy confirmed that Cu did not significantly modify the magnetic domains, indicating its effectiveness in decoupling MoS$_2$ from CoFeB. This decoupling preserves the spin-orbit coupling (SOC) of MoS$_2$ by mitigating the exchange interaction with CoFeB, as proximity to localized magnetization can alter the electronic structure and SOC. First-principles calculations revealed that Cu intercalation notably enhances the spin Berry curvature and spin Hall conductivity, contributing to the increased spin Hall angle. This study demonstrates that interface engineering of ferromagnet/TMD-based heterostructures can achieve higher spin-to-charge conversion efficiencies, paving the way for advancements in spintronic applications.

Enhancement of spin Hall angle by an order of magnitude via Cu intercalation in MoS$_2$/CoFeB heterostructures

TL;DR

The paper demonstrates that inserting a Cu spacer between MoS2 and CoFeB dramatically enhances spin-to-charge conversion by decoupling MoS2 from FM proximity effects, preserving its SOC. FMR-ISHE measurements reveal a spin Hall angle up to at nm, about an order of magnitude higher than MoS/CoFeB bilayers. Complementary MOKE and SQUID analyses confirm decoupling and improved spin-transport characteristics, while DFT-Wannier90 calculations show increased spin Berry curvature, intrinsic SHC, and higher MAE for the Cu-containing stack, consistent with SOC preservation. The results highlight interface engineering with interlayers as a viable route to high-efficiency spintronic devices and may extend to other TMD/FM systems.

Abstract

Transition metal dichalcogenides (TMDs) are a novel class of quantum materials with significant potential in spintronics, optoelectronics, valleytronics, and opto-valleytronics. TMDs exhibit strong spin-orbit coupling, enabling efficient spin-charge interconversion, which makes them ideal candidates for spin-orbit torque-driven spintronic devices. In this study, we investigated the spin-to-charge conversion through ferromagnetic resonance in MoS/Cu/CoFeB heterostructures with varying Cu spacer thicknesses. The conversion efficiency, quantified by the spin Hall angle, was enhanced by an order of magnitude due to Cu intercalation. Magneto-optic Kerr effect microscopy confirmed that Cu did not significantly modify the magnetic domains, indicating its effectiveness in decoupling MoS from CoFeB. This decoupling preserves the spin-orbit coupling (SOC) of MoS by mitigating the exchange interaction with CoFeB, as proximity to localized magnetization can alter the electronic structure and SOC. First-principles calculations revealed that Cu intercalation notably enhances the spin Berry curvature and spin Hall conductivity, contributing to the increased spin Hall angle. This study demonstrates that interface engineering of ferromagnet/TMD-based heterostructures can achieve higher spin-to-charge conversion efficiencies, paving the way for advancements in spintronic applications.

Paper Structure

This paper contains 6 sections, 9 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Experimental details
  3. Results and discussion
  4. Theoretical calculations
  5. Conclusion
  6. Acknowledgments

Figures (4)

  • Figure 1: (a) Measured dc voltage signals for 0$^\circ$ (open blue symbols) and 180$^\circ$ (solid black triangles) for sample M5 are shown as open circles. The solid red line is the fit to equation (1). The green and magenta lines are the $V_{sym}$ and $V_{asym}$ components of the voltage. (b) $\phi$ dependent $V_{sym}$ and $V_{asym}$ for samples M5, which are fitted to eqns. (2) and (3), respectively
  • Figure 2: (a) The voltage contributions due to spin pumping and other spin rectification effects as a function of $t_{Cu}$. $V_{sp}$ shows a dominating contribution over other rectification effects in all the samples. (b) Variation of $\theta_{SHA}$ as a function of $t_{Cu}$.
  • Figure 3: Domain images captured for samples M0 (a), M1 (b) and M5 (c) near to coercivity. Magnetic field direction shown in (a) is valid for all the domain images.
  • Figure 4: (a) Structural model for the MoS$_2$/Cu/CoFeB considered for the DFT-Wannier calculations for the spin transport. (b) Spin Berry conductivity as a function of energy relative to the Fermi energy, (c) the longitudinal charge conductivity as a function of the chemical potential.