Dead Layer in a Ta/Ni₈₁Fe₁₉/Ta Structure

Effect of Ta seed layers and Ta cap layers on the effective magnetic thickness of ultrathin permalloy (Ni₈₁Fe₁₉) was experimentally investigated for magnetic random access memory applications. The films were deposited by magnetron sputtering. For a Ta/Ni₈₁Fe₁₉/Ta fundamental structure, Ta seed and Ta cap layers resulted in a loss of moment equivalent to a magnetically dead layer of thickness 1.6±0.2nm. In order to find the mechanism, the composition and chemical states at the interface regions of Ta/Ni₈₁Fe₁₉ and Ni₈₁Fe₁₉/Ta were studied using the x-ray photoelectron spectroscopy and peak decomposition technique. The results show that there are thermodynamically favorable reactions at the Ta/Ni₈₁Fe₁₉ and Ni₈₁Fe₁₉/Ta interfaces: 2Ta+Ni=NiTa₂.