Structure of ultrathin Ni/Cu(001) films as a function of film thickness, temperature, and magnetic order

We report on a detailed structural study of ultrathin Ni films on Cu(100) applying quantitative low-energy electron diffraction. The analysis of films with different thickness shows that the film growth is pseudomorphic throughout the coverage regime investigated, 1-11 monolayers. The vertical spacings of the Ni layers, which are unreconstructed, are largely independent of both film thickness and depth. They are by about 3.2% contracted compared to the bulk spacings of Ni (5% compared to the bulk spacings of Cu), so that all films correspond to homogeneous tetragonal phases. Due to the tetragonal distortion, the volume of Ni atoms in the films is practically the same as in bulk Ni. The layer spacing at the Ni-Cu interface is slightly contracted compared to the value resulting from a hard sphere model, and the same holds for the top Cu layer distance. In particular, within the accuracy limits (1-2% or less) we detect no structural differences for the change from in-plane to vertical magnetization with varying coverage or temperature or for the change from ferro- to paramagnetism at the Curie temperature. [S0163-1829(99)03719-4].