High Frequency Spin Dynamics of Magnetic Tunneling Junctions Consisting of Two Perpendicular Free Layers*

Magnetic Tunnel Junctions (MTJ) with one fixed layer and one free layer have been extensively studied as a memory element, a microwave oscillator and a microwave detector. With the advent of harvesting interfacial perpendicular magnetic anisotropy (IPMA), perpendicular MTJs have drawn much recent attention over the prior sate of the art in-plane structures. We report our experimental investigation of MTJ structures with two perpendicular free-layers, with different strengths of IPMA. We find high frequency microwave emission can be produced at zero bias field when a small DC current is applied. We will show our understanding on mutual roles played by each IPMA layer. Micromagnetic simulations will be presented demonstrating the spin dynamics of the two free layers. The role of electron heating in these nanoscale structures, on the microwave emission spectrum, will be discussed. The work was supported by Center for Function Accelerated nano-Materials (FAME).