Controlling the demagnetizing field of an in-plane free layer by exchange coupling with a perpendicular multilayer

摘要

The demagnetizing field of a Co50Fe50 free layer in an in-plane micron-sized magnetic tunnel junction (MTJ) can be partially compensated by exchange coupling with a [Co90Fe10/Pt] N multilayer with perpendicular magnetic anisotropy via a Ru interlayer. The perpendicular anisotropy for N = 5 is optimized for nominal CoFe and Pt thickness of 0.4 nm and 1.0 nm, respectively. An increase of tunnel magnetoresistance (TMR) from 2% to 75% is observed in MTJs as the free layer thickness, t varies from 1.0 nm to 3.0 nm. A phenomenological model is developed to interpret the TMR dependence in terms of the free layer magnetization rotation from in-plane to out-of-plane with decreasing t, a consequence of interlayer exchange coupling with the perpendicular multilayer. We suggest that this strategy could significantly reduce the switching current density in such MTJs.