Dependence of tunnel magnetoresistance on ferromagnetic electrode   materials in MgO-barrier magnetic tunnel junctions
  We investigated the relationship between the tunnel magnetoresistance (TMR) ratio and the electrode structure in MgO-barrier magnetic tunnel junctions (MTJs). The TMR ratio in a MTJ with Co40Fe40B20 reference and free layers reached 355% at the post-deposition annealing temperature of Ta=400 degree C. When Co50Fe50 or Co90Fe10 is used for the reference layer material, no high TMR ratio was observed. The key to have high TMR ratio is to have highly oriented (001) MgO barrier/CoFeB crystalline electrodes. The highest TMR ratio obtained so far is 450% at Ta = 450 degree C in a pseudo spin-valve MTJ. 
Shoji Ikeda, Jun Hayakawa, Young Min Lee, Fumihiro Matsukura, and   Hideo Ohno