Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control

Area of Science:

• Spintronics
• Materials Science
• Condensed Matter Physics

Background:

• Efficient charge-to-spin conversion is vital for developing low-power spintronic devices like spin-orbit torque (SOT) magnetoresistive random access memories.
• Enhanced spin Hall conductivity in materials is a key factor for improving device performance.

Purpose of the Study:

• To investigate the impact of interface engineering and nanolayer insertions on spin Hall conductivity in epitaxial Ru/Cu heterostructures.
• To quantitatively evaluate the spin current generation and spin Hall efficiency in these engineered structures.

Main Methods:

• Fabrication of fully epitaxial Ru/Cu heterostructures with Cu/Ru nanolayer insertions.
• High-resolution high-angle annular dark-field scanning transmission electron microscopy for interface analysis.
• Measurement of unidirectional spin Hall magnetoresistance and spin-torque ferromagnetic resonance to evaluate spin Hall efficiency (ξDL).

Main Results:

• A sizeable spin Hall efficiency (ξDL) of -2.2% was observed in sharp Ru/Cu films.
• Insertion of Cu/Ru nanolayers increased the spin Hall efficiency to -3.7%.
• Achieved effective spin Hall conductivity of (3–5) × 10^5 ℏ2/eΩ−1m−1, comparable to platinum.

Conclusions:

• Interfacial control using hybrid nanolayer structures significantly enhances spin Hall conductivity in Ru/Cu systems.
• This approach enables the use of highly conductive metals with weak spin-orbit interactions for spintronic applications.
• The findings pave the way for developing stable, low-cost, and energy-efficient spintronic devices.