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 soft ferromagnetic electrode and 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\((\textit{x})\)/CoFeB/MgO\((\textit{y})\)/CoFeB\((\textit{z})\)/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 \(T_\textrm{ann}=330\,^{\circ}\)C for 60 min, while the interlayer exchange coupling and the saturation magnetization per unit area sharply decay at \(T_\textrm{ann}=340\,^{\circ}\)C for 60 min. Simultaneously, the tunnel magnetoresistance ratio shows a peak of \(65.5\%\) after being annealed at \(T_\textrm{ann}=300\,^{\circ}\)C for 60 min, with a significant reduction down to \(10\%\) for higher annealing temperatures (\(T_\textrm{ann}\geq330\,^{\circ}\)C) and down to \(14\%\) for longer annealing times (\(T_\textrm{ann}=300\,^{\circ}\)C for 90 min). We attribute the large decrease of tunnel magnetoresistance ratio to the loss of exchange bias in the pinned electrode.