The Influence of the Capping Layer on the Perpendicular Magnetic Anisotropy in Permalloy Thin Films

In this paper, we show that perpendicular magnetic anisotropy can be achieved in polycrystalline Ni₈₀Fe₂₀ films on MgO underlayers grown on thermally oxidized Si substrates. The perpendicular magnetic anisotropy is already present in the as-deposited films and preserved after thermal annealing. This paper points out the crucial role of the capping layer on the perpendicular magnetic anisotropy stabilization. By changing the nature of the capping from MgO, V, Nb to Ta, the value of the surface anisotropy constant is increased from 0.3 ± 0.05 erg/cm² in the case of the MgO to 0.79 ± 0.06 erg/cm² in the case of the Ta capping, respectively. For Ta capped samples, the perpendicular magnetization is achieved for Ni₈₀Fe₂₀ films with an effective thickness below 1.1 nm.