Spin Torque Nano-Oscillators with Tilted Magnetic Anisotropy

Abstract

Spin-torque nano-oscillators (STNOs) are promising nanoscale microwave oscillators for applications in wireless communication and neuromorphic computing. Although simulations suggest that STNOs with tilted magnetic anisotropy (TMA) can deliver superior performance, experimental investigations—especially those employing TMA free layers—remain unreported. Here, we experimentally investigate nanocontact STNOs (NC-STNOs) incorporating a TMA free layer based on a [Co/Pd]/Cu/[Co/Ni]/NiFe multilayer structure. By integrating experimental measurements with micromagnetic simulations, we uncover rich magnetization dynamics that are inaccessible in conventional anisotropy systems. Notably, we observe the coexistence and transition between distinct dynamical modes, which give rise to multi-frequency microwave emission. In addition, we identify a unique droplet-like propagating spin-wave (PSW) mode that simultaneously exhibits characteristics of both magnetic droplets and PSW. Most importantly, this droplet-like PSW mode enables synchronization over significantly greater distances compared to perpendicular magnetic anisotropy (PMA)-based STNOs, highlighting its potential for large-scale mutual synchronization. These findings advance the understanding of magnetization dynamics in TMA systems and establish a pathway toward synchronized STNO arrays for practical applications.