Effect of spacer material on the magnetic surface anisotropy in ultrathin Fe70B30 multilayer films

Abstract

It has been found recently that the magnetic surface anisotropy Ks in Fe70B30/Ag multilayer films decreases monotonically with magnetic layer thickness (2L) for 2L<16.5 Å. In order to determine possible effects of the spacer material on the surface anisotropy in the aforementioned system, Ag has been replaced with Al2O3 and ferromagnetic resonance (FMR) measurements have been made on these films. These Fe70B30/Al2O3 films were fabricated by magnetron sputtering and were characterized by X-ray-diffraction and vibrating sample magnetometer (VSM) measurements in addition to FMR. In the region where Ks depends upon 2L, the data is insufficient to confirm the thickness dependence of Ks that was observed in Fe70B30/Ag, while in the region where Ks is independent of 2L, the values of Ks deduced for Fe70B30/Ag and Fe70B30/Al2O3 are in good agreement. The latter is particularly interesting in light of the enormous difference in conductivity between Ag and Al2O3.