Interface stability between amorphous ferromagnetic layer and Al oxide barrier in tunneling magnetoresistive films at elevated temperatures

The interface stability and microstructure between amorphous and crystalline ferromagnetic (FM) layers Fe₅₆Co₂₄B₂₀ and Co₇₀Fe₃₀ (at. %) and oxide barrier layers (AlO) deposited by physical vapor deposition, in both as-deposited and annealed states, have been studied using hysteresis loops for magnetic measurement, x-ray photoelectron spectroscopy for elemental depth profiling, and transmission electron microscopy for atomic-level microstructure. AlO was found to be amorphous on both amorphous Fe₅₆Co₂₄B₂₀ and polycrystalline Fe₃₀Co₇₀ FM layers. Substantial Fe diffusion towards the AlO layer and Al diffusion towards the FM layer are clearly observed for the Fe₅₆Co₂₄B₂₀/AlO system when annealed above 360 °C and will likely cause magnetic tunneling junction devices made from this system to fail.