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

Abstract

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=0.3nm. For stacks with z=1.05nm, the magnetic properties of the soft electrode resemble the characteristics of superparamagnetism. For stacks with x=0.4nm, y=2nm, and z=1.20nm, the exchange bias presents a significant decrease at post-annealing temperature Tann=330°C for 60 min, while the interlayer exchange coupling and the saturation magnetization per unit area sharply decay at Tann=340°C for 60 min. Simultaneously, the tunnel magnetoresistance ratio shows a peak of 65.5% after being annealed at Tann=300°C for 60 min, with a significant reduction down to 10% for higher annealing temperatures (Tann≥330°C) and down to 14% for longer annealing times (Tann=300°C for 90 min). We attribute the large decrease of tunnel magnetoresistance ratio to the loss of exchange bias in the pinned electrode.