All Perpendicular Spin Nano-Oscillators with Composite Free Layer

Owing to improved thermal stability and scalability, materials with perpendicular magnetic anisotropy (PMA) are extremely attractive. The all perpendicular magnetic tunnel junction (p-MTJ) devices are primarily devoted to spin transfer torque (STT)-induced switching and few works report their microwave emission. Here, we demonstrate the basic results of RF function in nanoscale p-MTJ which has two different thickness free layers separated by atom-thick tungsten insertion. The ultrathin W spacer layer not only enables the two CoFeB free layers precess as a single layer but also greatly enhances the PMA which further induces high-emission frequency. The all perpendicular spin transfer torque nano-oscillator (STNO) exhibited high frequency (7.6 GHz) and large current modulation capability of 0.86 GHz · mA^-1 at moderate external magnetic field. Along with our previous work on STT switching utilizing the similar stack, such a multifunctional structure could bring low cost solutions to Internet of Things (IoT) network applications.