Effect of annealing on the local structure of Fe and Co in CoFeB/MgO based magnetic tunnel junction: An extended X-ray absorption fine structure study

The evolution of the local structure of Fe and Co as a function of annealing time in CoFeB/MgO/CoFeB magnetic tunnel junctions was studied using extended x-ray-absorption fine structure (EXAFS). EXAFS indicates B depletion and crystallization of the CoFeB layers within a few seconds of the post growth high temperature anneal. The decrease in first-shell Debye--Waller factor and hence the increase in structural order during annealing explains the increase in tunnel magnetoresistance observed as a result of post deposition annealing. Although the diffusion of B has also been confirmed by several other experiments, there has not been much consensus on where the B diffuses after high temperature anneal. Recent results from B Near edge x-ray absorption fine structure (NEXAFS) will also be discussed.