Analysis of a Spin-Torque Oscillator Using Injection Locking to an External Microwave Field

A spin-torque oscillator (STO) is a key device in microwave-assisted magnetic recording (MAMR). Conventionally, the magnetization dynamics of STOs has been analyzed using the high-frequency electrical signal from the STO (STO signal). However, the STO signal is sometimes undetectable because of the highly symmetric magnetization trajectory or contains several frequency components that do not correspond to the frequency of the actual magnetization oscillation [1] . Furthermore, when the STO is integrated into the write head, the STO signal is expected to attenuate heavily in the write head, making it difficult to extract the STO signal. These facts prevent identifying the oscillation frequency from the STO signal, and a new analysis method of the STO that does not rely on the STO signal is required.