Perpendicular magnetic tunnel junctions using Co-based multilayers

CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA) free and reference layers composed of Co/M (where M=Pd or Ni) multilayers have been optimized for high PMA and high tunneling magnetoresistance (TMR). The effects of Co thickness, Pd thickness, and the number of Co/Pd bilayers on the anisotropy and coercivity of the [Co/Pd](n) multilayer films have been studied for both free and reference layers. The damping parameter alpha of CoFeB capped multilayers was determined using broadband ferromagnetic resonance. The transport properties of the patterned MTJ stacks were measured from 10 to 400 K. A maximum TMR of 10% at 10 K (5%-10% at 300 K) was obtained for these perpendicular MTJs, regardless of whether or not they were magnetically annealed for MgO-CoFeB crystallization. This indicates that the fcc-bcc-fcc transitions from the fcc multilayers to the bcc CoFeB/MgO/CoFeB do not promote the "giant MgO TMR effect" caused by symmetry filtering. (C) 2010 American Institute of Physics. [doi:10.1063/1.3358242]