Magnetic noise evolution in CoFeB/MgO/CoFeB tunnel junctions during annealing

We report on the evolution of equilibrium magnetoresistive (MR) 1/f noise due to the exchange-biased magnetic layer in MgO-based magnetic tunnel junctions as a function of annealing time at 380 and 430 °C. The resistance susceptibility and MR noise are observed to increase rapidly with annealing time at a fixed temperature. The magnetic losses responsible for MR noise are not significantly affected by the structural crystallization at the CoFeB/MgO interface during short annealing times. After prolonged annealing, the decrease in magnetic losses is attributed to reduced disorder in the magnetic layers that result in thermally driven fluctuations in local micromagnetic structure.