Material parameters of perpendicularly magnetized tunnel junctions from spin torque ferromagnetic resonance techniques

Abstract

The exchange-stiffness and saturation magnetization for the CoFeB based free layer of perpendicularly magnetized tunnel junctions (MTJs) were determined by performing spin torque ferromagnetic resonance measurements over a range of different sized devices. The field dispersion of several low-frequency spin wave modes shows a size dependent shift in the resonance frequencies due to the change in the lateral confinement and demagnetization field. From the effect of the demagnetizing field, the free layer saturation magnetization is estimated to be ∼800 emu/cm3 and its total perpendicular anisotropy field ∼12 kOe. From the separation of spin wave dispersion relations, an exchange stiffness value of 0.35 eV Å2 is extracted.