Magnetization, Curie temperature, and magnetic anisotropy of strained (111) Ni/Au superlattices.

Abstract

The magnetic properties of well-characterized strained (111) Ni/Au superlattices with bilayer thickness \ensuremath{\Lambda}5 nm are examined as a function of Ni layer thickness ${\mathit{d}}_{\mathrm{Ni}}$. The saturation magnetization of Ni is found to decrease inversely with ${\mathit{d}}_{\mathrm{Ni}}$, while the decrease in Curie temperature ${\mathit{T}}_{\mathit{C}}$ follows a power law. Superlattices grown on 625-K substrates show larger magnetization, higher ${\mathit{T}}_{\mathit{C}}$, and lower magnetic anisotropy than ones grown at room temperature. In both cases, an abrupt decrease in the anisotropy is found at the same \ensuremath{\Lambda} where a coherent-to-incoherent transition is observed in structural studies. Additional structural data indicate that, in this thickness region, the Ni layers are strongly strained both parallel and perpendicular to the growth direction, and thus do not follow conventional elastic behavior. This underlines the importance of an accurate determination of the structural properties when analyzing the magnetic properties of short-period metallic superlattices.