A magnetic read sensor having improved magnetic performance and robustness. The magnetic sensor includes a magnetic free layer and a magnetic pinned layer structure. The magnetic pinned layer structure includes first and second magnetic layers separated from one another by a non-magnetic coupling layer. The second magnetic layer of the magnetic pinned layer structure includes a layer of CoFeBTa, which prevents the diffusion of atoms and also promotes a desired BCC crystalline grain growth. The magnetic free layer structure can also include such a CoFeBTa layer for further prevention of atomic diffusion and further promotion of a desired BCC grain growth.