Interface reactions in Ta/Ni81Fe19/Ta structures and their influence on magnetic properties

Ta/Ni81Fe19, Ni81Fe19/Ta, Cu/Ni81Fe19, and Ni81Fe19/Cu structures are commonly used in the magnetic multilayers with giant magnetoresistance. For a Ta/Ni81Fe19/Ta fundamental structure, Ta seed and Ta cap layers result in a loss of moment equivalent to a magnetically dead layer of thickness 1.6 ± 0.2 nm. Experimental results show that a chemical reaction between Ta and Ni81Fe19 takes place at the Ta/Ni81Fe19 and Ni81Fe19/Ta interfaces. The thickness of the magnetically dead layer was significantly reduced by the insertion of a small amount of Bi in the Ta/Ni81Fe19/Ta structure (i.e. Ta/Bi/Ni81Fe19/Ta). This result indicates that Bi acts as a surfactant that can suppress the interface reaction in multilayers. For a Cu/Ni81Fe19/Cu film, permalloy layers have hardly lost their magnetic moment since interface reactions at the Cu/Ni81Fe19 interface or Ni81Fe19/Cu interface hardly occurs.