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.