Magnetization reversal and enhanced tunnel magnetoresistance ratio in perpendicular magnetic tunnel junctions based on exchange spring electrodes

The [Co / Pt] n multilayer based perpendicular magnetic tunnel junction stacks with wedged Co 60 Fe 20 B 20 insertions up to 2 nm, and corresponding perpendicular magnetic tunnel junctions were magnetically and electrically investigated. The focus is on the influence of CoFeB insertions in the free and reference electrodes on the overall junction magnetization reversal and magnetoresistance response. The exchange spring behavior was revealed as the Co 60 Fe 20 B 20 spins canting towards the in-plane direction in the [Co / Pt] n / Co 60 Fe 20 B 20 hard/soft perpendicular magnetic electrodes. The broad range thickness of wedged Co 60 Fe 20 B 20 insertion enables to reveal the critical transition, in particular, from rigid coupling to exchange spring coupling. With the help of 375°C annealing under 10 kOe magnetic field, the recovery from distinct multi-domain structure to nearly single domain structure was distinctly observed in the unpatterned perpendicular magnetic tunnel junction (p-MTJ) films with CoFeB thickness t CFB ≥ 1.5 nm. Meanwhile, for the corresponding patterned perpendicular magnetic tunnel junctions with AlO x barrier, the tunnel magnetoresistance (TMR) ratio exhibited an intense enhancement over 100%. The TMR results and spin configurations were illustrated using an exchange spring model in both magnetic electrodes. The presented study shows the benefit of using exchange spring magnetic electrodes in perpendicular magnetic tunnel junction on their performance.