Tunnel Magnetoresistance Properties of Double MgO-Barrier Magnetic Tunnel Junctions With Different Free-Layer Alloy Compositions and Structures

We investigated tunnel magnetoresistance (TMR) properties in double MgO-barrier magnetic tunnel junctions (DMTJs) with (Co
₂₅
Fe
₇₅
)
_100-x
B
_x
free-layers with
x
= 15, 20, and 25 (in at.%) sputtered at different power. The TMR ratio of DMTJs increased with sputtering power, which is ascribed to the B composition reduction in the CoFeB free-layer with increasing sputtering power. The x-ray diffraction measurement showed that crystallization into (001)-oriented texture of CoFeB film sandwiched between the two MgO-layers as well as an improvement of (001) orientation of top MgO-barrier are realized. The TMR ratio over 200% was obtained in DMTJs with a (Co
₂₅
Fe
₇₅
)
₈₅
B
₁₅
free-layer sputtered at 0.88 and 1.77 W/cm
²
.