Analysis method of a spin-torque oscillator using dc resistance change during injection locking to an external microwave magnetic field

Spin torque oscillators (STOs) that generate a persistent magnetization oscillation by spin-transfer torque are promising spintronic devices for various applications. In this study, we propose and experimentally demonstrate a method to characterize the magnetization dynamics of STOs using injection locking. By placing the STO near an antenna that generates a microwave magnetic field of a variable frequency ( f M W), injection locking of the STO to the microwave field occurs when f M W is in the locking range around the intrinsic oscillation frequency. During injection locking, the dc resistance of the STO exhibits a peak-and-valley dependence on f M W, which originates from the modification of the magnetization trajectory induced by injection locking. Based on this principle, the oscillation frequency can be estimated by measuring the dc resistance change. Because this method does not require measuring the high-frequency magnetoresistance signal from the STO, which is used in the conventional method, it is advantageous in cases where the high-frequency magnetoresistance signal is undetectable or exhibits additional frequency components different from the oscillation frequency.

Automated summary

In this study, a new method is proposed to characterize the magnetization dynamics of STOs using injection locking with a microwave antenna. By observing the peak-and-valley dependence of the dc resistance, the oscillation frequency of the STO can be estimated without the need for high-frequency magnetoresistance measurements.