Spin-dependent migration-conduction model for ultra-thin magnetic tunnel junctions

Magnetic-tunnel junctions MTJs with ultra-thin (∼6–9 Å) oxide barriers, having the resistance-area product as low as 1–10 Ω μm 2, and magnetoresistance as high as ∼20%, were studied. In the temperature range from 300 to 25 K, they display resistance combined between metallic and activated laws. Under applied currents from 0.1 to 10 mA, the dynamic conductance varies from chaotic to periodic regimes, and the noise power spectrum over times from 10 ms to 10 5 s shows a crossover from 1/ f 2 to 1/ f behavior, all the features being different for parallel (P) and antiparallel (AP) magnetization of electrodes. A theoretical model is proposed, combining electron tunneling through localized defect states in the barrier and migration of respective defect atoms. A qualitative agreement with the experimental noise spectrum is achieved.