Correlation of tunnel magnetoresistance with the magnetic properties in perpendicular CoFeB-based junctions with exchange bias.

We investigate the dependence of magnetic properties on the post-annealing temperature/time, the thickness of the soft ferromagnetic electrode, and the Ta dusting layer in the pinned electrode as well as their correlation with the tunnel magnetoresistance ratio, in a series of perpendicular magnetic tunnel junctions of materials sequence Ta/Pd/IrMn/CoFe/Ta(x)/CoFeB/MgO(y)/CoFeB(z)/Ta/Pd. We obtain a large perpendicular exchange bias of 79.6 kA/m for x = 0.3 nm. For stacks with z = 1.05 nm , the magnetic properties of the soft electrode resemble the characteristics of superparamagnetism. For stacks with x = 0.4 nm , y = 2 nm , and z = 1.20 nm , the exchange bias presents a significant decrease at post-annealing temperature T ann = 330 ° C for 60 min, while the interlayer exchange coupling and the saturation magnetization per unit area sharply decay at T ann = 340 ° C for 60 min. Simultaneously, the tunnel magnetoresistance ratio shows a peak of 65.5 % after being annealed at T ann = 300 ° C for 60 min, with a significant reduction down to 10 % for higher annealing temperatures (T ann ≥ 330 ° C) and down to 14 % for longer annealing times (T ann = 300 ° C for 90 min). We attribute the large decrease of tunnel magnetoresistance ratio to the loss of exchange bias in the pinned electrode. [ABSTRACT FROM AUTHOR]