It has been reported that in a CoFeB$/$MgO$/$CoFeB based tunnel junction, B diffuses into the MgO layer. In this work we consider three possible locations of B in the MgO lattice upon diffusing into the MgO crystal: B substitutes for an Mg site, it substitutes for an O site, or it occupies an interstitial position. Apart from the possibility of introducing midgap states, various charge states of the defect could sustain a local magnetic moment. This could additionally modify the tunnel magneto-resistance ratio. We investigate the electronic structure, the local moment formation, and the formation energies of various defect states. While midgap states are introduced in all three cases, the low formation energy defects are found to be nonmagnetic.

• Received 8 May 2013
• Revised 26 February 2014

DOI:https://doi.org/10.1103/PhysRevB.89.144412