The effect of Ta seed layers and Ta cap layers on the effective magnetic thickness of ultrathin permalloy (Ni81 Fe19)was experimentally investigated for magnetic random access memory applications. The films were deposited by magnetron sputtering. For a Ta/Ni81Fe19/Ta fundamental structure, the Ta seed and Ta cap layers resulted in a loss of moment equivalent to a magnetically dead layer of thickness 1.6 ± 0.2 nm. In order to find the mechanism, the composition and chemical states at the interface regions of Ta/Ni81 Fe19 and Ni81 Fe19/Ta were studied using x-ray photoelectron spectroscopy and the peak decomposition technique. The results show that there are thermodynamically favourable reactions at the Ta/Ni81 Fe19 and Ni81Fe19/Ta interfaces: 2Ta + Ni = NiTa2.