The dependency of tunnel magnetoresistance ratio on nanoscale thicknesses of Co2Fe6B2 free and pinned layers for Co2Fe6B2/MgO-based perpendicular-magnetic-tunnel-junctions

Abstract

The tunnel magnetoresistance (TMR) ratio of a cobalt-iron-boron (CoFeB)-based perpendicular-magnetic-tunnel-junction (p-MTJ) spin valve is extremely sensitive to both nanoscale Co2Fe6B2 free-and pinned-layer thicknesses. The TMR ratio peaks at a Co2Fe6B2 free-layer thickness of 1.05 nm, while it peaks at a Co2Fe6B2 pinned-layer thickness of 1.59 nm, achieving 104%. The amount of tantalum diffused into the MgO tunneling barrier (originated from a tantalum seed) decreases with increasing Co2Fe6B2 free-layer thickness, while the amount of palladium diffused from a [Co/Pd](n) SyAF layer decreases with increasing Co2Fe6B2 pinned-layer thickness, determining the crystallinity of the MgO tunneling barrier and the TMR ratio. In addition, the TMR ratio tended to decrease when the Co2Fe6B2 free layer and the Co2Fe6B2 pinned layer switched characteristics from interface-perpendicular anisotropic to in-plane anisotropic.