High-Efficiency Continuous Spin-Conduction through NiO/Cu Bilayer Structure.

Area of Science:

• Spintronics
• Materials Science
• Nanotechnology

Background:

• Spin-orbit torque (SOT) devices are vital for nanomagnet memory.
• Efficient charge and spin current separation is critical for SOT device performance.
• Nickel oxide (NiO) is an insulating material with spin-conducting properties relevant for these devices.

Purpose of the Study:

• To investigate the effectiveness of a spin-transparent copper (Cu) layer in facilitating spin current transmission through NiO.
• To analyze the impact of NiO thickness on spin current conduction in a Pt/NiO/Cu/NiFe stack.
• To demonstrate the potential for improved charge-spin separation and device reliability in spintronic applications.

Main Methods:

• Fabrication of nanobridges from Pt/NiO/Cu/NiFe multilayer stacks with varying NiO thicknesses.
• Utilizing dc bias-dependent spin-torque ferromagnetic resonance (ST-FMR) to measure spin-current conduction.
• Characterizing the spin-transparency and transmission efficiency of the Cu spacer and NiO layers.

Main Results:

• A highly spin-transparent Cu spacer (93% efficiency) was confirmed.
• Over 40% spin current transmission was achieved through defect-free NiO/Cu bilayers for NiO thicknesses greater than 1.5 nm.
• The Pt/NiO/Cu/NiFe stack demonstrated effective charge-current confinement and spin-current transmission.

Conclusions:

• The incorporation of a Cu layer significantly enhances spin current transmission across NiO, improving charge-spin separation.
• This approach ensures a uniform magnetic environment and prevents unwanted exchange interactions, leading to enhanced device reliability.
• The demonstrated seamless spin-torque conversion from magnonic to electronic transport opens avenues for novel spin-current-based device designs.