Co/Fe Multilayers With Ultra-Low Damping And Large Negative Anisotropy As The Free Layer For Spin Torque Oscillator

We have investigated the characteristic properties of Co/Fe multilayers sputtered on Ru underlayer as the field generation layer (FGL) of spin torque oscillator (STO) for microwave assisted magnetic recording. The Co/Fe multilayers exhibit large uniaxial negative anisotropy (up to similar to 8.7 x 10(6) erg/cm(3)), ultra-low damping constant (similar to 0.008), and small in plane coercivity H-c (similar to 5 Oe) that are required for stable STO precession over a wide range of applied magnetic fields and injected spin currents. The importance of Ru underlayer to achieve the above parameters has been addressed. We further show through theoretical calculations that a frequency of 30+ GHz is realistic using Co/Fe multilayers as the field generation layer in a STO comprising a perpendicularly magnetized polarizer and a planar FGL (10-nm Co/Fe multilayers) separated by a metallic spacer. Published by AIP Publishing.