Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Tunnel magnetoresistance was measured in CoFeB-MgO-based double-barrier magnetic tunnel junctions. Variation of the sputtering power density is used to control the relative B content of the middle electrode. Magnetoresistance ratios in both upper and lower junctions are suppressed with respect to the single-barrier case. While the lower junction shows a saturation of the magnetoresistance as a function of high temperature annealing for all sputtering power densities, the upper junction exhibits an increase in magnetoresistance as a function of annealing temperature with higher values for higher sputtering power density. The suppression of high magnetoresistance is attributed to a lack of strong crystallisation in the middle electrode, which is confirmed by cross-section transmission electron microscopy. Slight crystallisation of the middle electrode is achieved at the highest sputtering power density despite that fact that boron diffusion is suppressed due to the adjacent MgO tunnel barriers. Optimal deposition and post annealing conditions resulted in magnetoresistance values of 140 % and 80 % for the upper and lower junctions, respectively.