Abstract
Exchange-biased dual spin-valve type magnetic double tunnel junctions (DSV-MTJs) of Ir-Mn/Co-Fe/AlOx/Co-Fe/AlOx/Co-Fe/Ir-Mn were annealed at 175-400°C. After annealing at 325°C, the magnetoresistance (MR) ratio and bias voltage Vh, at which the MR ratio is reduced by 50%, in the DSV-MTJs were greatly increased to 42% and 930 mV, respectively. After annealing above 325°C, the MR ratio and Vh decreased. This degradation of DSV-MTJs annealed above 325°C was investigated using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The XPS spectra and TEM images showed that an AlOx/MnOx composite tunnel barrier was formed due to the diffusion of Mn through the Co-Fe layer and oxygen redistribution above 300°C. Taking into account the spin-independent two-step tunneling via defect states in the barrier, we considered that this AlOx/MnOx composite barrier leads to decreasing the MR ratio and Vh and increasing the tunnel resistance.
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