Abstract
Spin-torque oscillators are promising candidates for hard disk drive read head sensors, neuromorphic computing, and telecommunications due to their frequency tunability by a direct current or a magnetic field. A narrow linewidth and a large quality factor are of great importance for these applications. Previous studies have indicated that the spin-torque oscillation linewidth depends on the temperature, current, and in-plane field angle. Here, we have investigated the spin-torque oscillations in MgO-based magnetic tunnel junctions (MTJs) and demonstrated the impact of the MTJ shape anisotropy on the threshold current. Our experimental results suggest that due to different threshold currents, the linewidth is different in the MTJs with different shape anisotropy, which might be significant for device optimization.
Highlights
Since the discovery of spin-transfer torque (STT) effect,1–4 spin-torque oscillators (STOs) have been extensively studied due to their numerous potential applications including tunable microwave oscillators,5–8 hard disk drive read head sensors,9 neuromorphic computing,10–12 parallel microwave signal processors,13 and wireless communications.14–16 STO devices utilize the spin torque generated by a spin-polarized current to drive persistent magnetization precession
Taking the impedance mismatch into consideration, we define the pulse amplitude by 2VZ/(Z + Z0), where V is the output voltage pulse of the pulse generator, Z is the impedance of the magnetic tunnel junctions (MTJs), and Z0 is the impedance of the circuit
From the extrapolation of the linear fits to the zero linewidth, we find the threshold currents of devices A, B, and C to be Ith ≈ 0.34, 0.29, and 0.22 mA, respectively
Summary
Since the discovery of spin-transfer torque (STT) effect, spin-torque oscillators (STOs) have been extensively studied due to their numerous potential applications including tunable microwave oscillators, hard disk drive read head sensors, neuromorphic computing, parallel microwave signal processors, and wireless communications. STO devices utilize the spin torque generated by a spin-polarized current to drive persistent magnetization precession. Spin-torque oscillations have been observed in giant magnetoresistive (GMR) spin valves and MgO-based magnetic tunnel junctions (MTJs).. The precession of the free layer magnetization leads to a microwave oscillatory component of the device resistance, an oscillatory component of the output power. Compared to traditional semiconductor-based oscillators, the nanoscale spin-torque oscillators have their unique advantages. They are small, frequency tunable, with a wide working temperature range, and are compatible with complementary metal-oxide- semiconductor (CMOS) processes.. The desired microwave signal should be with high output power, narrow linewidth, and tunable frequency.. The linewidth discussed later in this paper is about the two-state switching contribution of the thermal noise only. Scitation.org/journal/adv which influences the linewidth of spin-torque oscillations excited in nanopillar MgO-based MTJ samples
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