Bulk Spin-Orbit Torque-Driven Spin Hall Nano-Oscillators Using PtBi Alloys with Engineered Crystallinity.

Area of Science:

• Spintronics
• Materials Science
• Nanotechnology

Background:

• Spin-orbit-torque-driven auto-oscillations in spin Hall nano-oscillators (SHNOs) are key for energy-efficient nanoscale microwave devices.
• Lowering the threshold current (I_th) is crucial for robust SHNO oscillations, but conventional methods to enhance spin Hall efficiency (θ_SH) have drawbacks.

Purpose of the Study:

• To enhance the bulk spin Hall effect in PtBi alloys through crystallographic engineering.
• To reduce the threshold current and improve performance metrics of SHNOs.

Main Methods:

• Crystallographic engineering of PtBi alloys.
• DC-bias spin-torque ferromagnetic resonance to extract spin Hall efficiency.
• Fabrication and characterization of 100 nm SHNOs using CoFeB/PtBi heterostructures.

Main Results:

• Achieved a 3-fold increase in spin Hall efficiency (θ_SH) in PtBi alloys (up to 0.24) compared to pure Pt (0.07).
• Reduced threshold current (I_th) by 42% and 32% in SHNOs utilizing PtBi alloys.
• Observed narrower linewidths (~25 MHz), enhanced quality factors (up to 550), and a 61.6% reduction in threshold power.

Conclusions:

• PtBi alloys are efficient spin Hall materials, enabling significant performance improvements in SHNOs.
• This advancement facilitates reduced power consumption for SHNO-based neuromorphic and memory technologies.