High power and low critical current density spin transfer torque nano-oscillators using MgO barriers with...

Area of Science:

• Spintronics
• Condensed Matter Physics
• Microwave Engineering

Background:

• Magnetic tunnel junction (MTJ)-based spin transfer torque nano-oscillators (STNOs) typically require very thin insulating barriers (R×A ~1 Ωμm²) for efficient microwave emission.
• The role of the tunnel barrier's properties in STNO dynamics has been less explored compared to magnetic configurations.

Purpose of the Study:

• To investigate the impact of thicker insulating barriers on the performance of STNOs with in-plane magnetized free layers.
• To explore methods for enhancing output power (Pout) and reducing critical current density (JSTT) in STNOs.

Main Methods:

• Fabrication and characterization of STNOs with varying insulating barrier thicknesses, leading to higher resistance-area (R×A) products (7.5–12.5 Ωμm²).
• Measurement of steady-state microwave emission, output power, oscillation linewidth (Γ), and critical current density (JSTT).

Main Results:

• Achieved output powers (Pout) up to 200 nW, a significant increase from the typical 1–40 nW range.
• Demonstrated sustained self-oscillation and maintained signal linewidth (Γ) despite using thicker barriers.
• Observed a two-order-of-magnitude reduction in critical current density (JSTT) for spin transfer torque induced dynamics.

Conclusions:

• Thicker insulating barriers in MTJ-based STNOs can lead to substantially higher microwave output power.
• The tunnel barrier's properties play a crucial role in STNO dynamics, offering a new avenue for device optimization.
• These findings pave the way for more efficient and powerful spintronic nano-oscillator devices.