Effect of capping layer material on tunnel magnetoresistance in CoFeB-MgO-CoFeB magnetic tunnel junctions

The effect of capping layer (CL) material on tunnel magnetoresistance (TMR) and magnetic properties in CoFeB/MgO/CoFeB magnetic tunnel junctions has been studied. The use of CL materials such as Ta, Ru, PtMn, Mg and IrMn yielded high MR ratio of more than 100%. The use of ferromagnetic materials, on the other hand, such as NiFe, CoFe or Fe decreased the MR ratio, as well as using Al, Cu, NiFeCr or Ir. The dependence of coercivity on CL materials for the same samples are also studied. It was speculated from the results that the degradation of the TMR and the magnetic properties when particular capping layer materials were used, is due to the formation of a reactive layer between the free layer and the capping layer.