The Microwave Emission Mode of Magnetic Tunnel Junction Nano-oscillators Controlled by the In-plane Magnetic Field

The spin-transfer nano oscillator (STNO) is a potential candidate as a neuromorphic device for their nonlinear dynamic characteristics. However, there is a lack of research on the precessional properties and controllability of STNO in the application of neuromorphic devices. Therefore, the STNO microwave emission modes and the regulation characteristics of an in-plane magnetic field with various orientations were studied in this paper. The power spectral density of STNO microwave emission was measured and analyzed, and a single to double mode oscillation was observed as the change of magnetic field angle. Furthermore, the precessional mode strongly correlates with the magnetoresistance, indicating that the conversion from single to double mode precessional appeared before the free layer switching. This phenomenon is attributed to the incoherent local magnetization precession when the device is in a latent critical unstable. Based on the above results, several preliminary ideas for building new types of neuromorphic devices, which are beneficial for the STNO application in neuromorphic devices, were proposed.