Effect of bias voltage and interdiffusion in Ir-Mn exchange-biased double tunnel junctions

Dual-spin-valve-type double tunnel junctions (DTJs) of sputtered Ir-Mn/Co-Fe/AlO_x/Co₉₀Fe₁₀ /AlO_x/Co-Fe/Ir-Mn having the R(resistance) × A(area) product; RAP ∼ 3.0 kΩ-μm² were fabricated and annealed at various temperatures (150-400°C) to introduce interdiffusion. There is a relation between the loss of the magnetoresistance (MR) ratio and that of dc bias voltage value at which the MR ratio decreases in half value (V_1/2). After annealing at 300°C, both the MR ratio and V_1/2 were increased to 42.4% and 872 mV, respectively, with increasing annealing temperature. Annealing above 300-350°C, both MR ratio and V_1/2 decreased rapidly. The loss of the MR ratio and that of V_1/2 are well explained by considering interdiffusion of O and Mn at the AlO_x/Co-Fe/Ir-Mn interfaces. The mechanism for the loss of MR ratio is not only related to the loss of interface polarization, but is also related to the barrier properties, taking into account the spin-independent two-steps tunneling via defect states in the barrier. These results are consistent with the X-ray photoelectron spectroscopy and cross-sectional transmission electron spectroscopy measurements, which indicate the existence of an Al-Mn-O barrier above 300°C.