Induced uniaxial magnetic anisotropy and film magnetostriction in very thin permalloy films

The induced uniaxial anisotropy field H_k in very thin films sandwiched by Ta or Cu layers was investigated. The value of H_k of the Ta/Cu/Ni₇₉Fe₂₁/Cu/Ta film decreases as film thickness decreases below 20 nm, even after an annealing procedure in a magnetic field. This H_k reduction is similar to that of the Ta/Ni₇₉Fe₂₁/Ta films, indicating that the H_k reduction is independent of surface energy and/or crystal structure of seed layers. The value of film magnetostriction λ_p-p of the Ta/NiFe/Ta films gradually increases as the thickness decreases, which is coincident with the reduction of H_k. However, the increase of the λ _p-p values, by decreasing Ni concentration or annealing the films, resulted in conflicting H_k values. These results indicate that the H_k reduction in thin films is not simply caused by the magnetostrictive effect