High inverted tunneling magnetoresistance in MgO-based magnetic tunnel junctions

Inverted tunneling magnetoresistance, where resistance decreases as the free layer in a magnetic tunnel junction flips its direction of magnetization after saturation, has been observed at zero bias in magnetic tunnel junctions with a thin CoFeB layer in the pinned synthetic antiferromagnetic CoFe∕Ru∕CoFeB stack. Magnetoresistance values as high as −55% at room temperature are measured in MgO-based tunnel junctions when the thickness of the pinned CoFeB layer is 1.5nm. The inverted magnetoresistance is associated with imbalance of the synthetic antiferromagnetic pinned layer. Asymmetric bias dependence with a magnetoresistance sign change is observed for a 0.5nm pinned CoFeB layer.