Zero-Field Spin Torque Oscillator Based on Magnetic Tunnel Junctions with a Tilted CoFeB Free Layer

Microwave emission from spin torque oscillators based on CoFeB/MgO/CoFeB magnetic tunnel junctions is analyzed with respect to the thickness of the magnetically free electrode. Taking advantage of the ferromagnetic interlayer exchange coupling between the free and reference layers and the perpendicular interface anisotropy of thin CoFeB electrodes on MgO, we demonstrate that large-amplitude oscillations of the tilted CoFeB free layer can be generated in zero applied magnetic field. (C) 2012 The Japan Society of Applied Physics