Induced uniaxial magnetic anisotropy field in very thin NiFe and CoZrNb films

The induced uniaxial anisotropy field in thin permalloy and CoZrNb films was investigated. The value of the induced anisotropy field H_k of permalloy films of 77-81 at%Ni concentration was found to decrease as the film thickness decreased below 20 nm, even after annealing procedure in a magnetic field. The value of H_k at 3 nm was found to be nearly half that at 20 nm. A series of CoZrNb amorphous films showed a qualitatively similar thickness dependence of N _k. Moreover, a similar reduction of H_k was observed at 77 K. On the other hand, the easy axis of Ni₇₉Fe ₂₁ films thinner than 20 nm was switched to the field direction by annealing with a magnetic field perpendicular to the easy axis of the as-deposited films, even at a low annealing temperature of 160°C. The absolute value of H_k in the 3 nm film after annealing at 160°C was nearly as large as in the as-deposited film. It is likely that the rearrangement of atom pairs can easily occur in the surface region, resulting in the switching of the easy axis to the annealing field direction in very thin films