Detection of small magnon fluctuations using parametric excitation process

Magnon amplification is a crucial research topic in spintronics. Magnons serve as carriers in spintronic devices, and their amplification can significantly enhance device performance. Several methods based on spin-transfer torque and parametric nonlinearity have been explored to achieve this. Recently, the increasing interest in the nonlinear and quantum properties of magnons has emphasized the need to amplify and detect small magnon fluctuations, where these characteristics are especially prominent. However, methods for detecting such small magnon fluctuation dynamics are not yet fully developed.

In this study, we report a 43 dB phase-sensitive magnon amplification achieved through the time evolution of parametric excitation. This amplification allows for the detection of small magnon fluctuations that are typically obscured by circuit noise in conventional measurements. Parametric excitation, a nonlinear process, induces magnetization precession at frequency f using an a.c. magnetic field at frequency 2f. If precession exists prior to excitation, its amplitude and fluctuations increase, effectively amplifying the process. We demonstrate the amplification of magnon fluctuations and provide a systematic evaluation of the amplifier noise in this process.