Thin tetragonally strained fcc-Co films grown epitaxially on Cu(001) single crystals have been investigated by ${}^{59}\mathrm{Co}$ nuclear magnetic resonance (NMR). The ultrahigh structural quality and the homogeneity of the strain result in the direct NMR observation of electric-field gradients, which is unique in thin films. The structural quality and the homogeneity and size of the strain are analyzed by means of the very small NMR linewidths, the hyperfine field anisotropies, and the uniform electric-field gradients. A quantitative agreement with the observed strain is found. The strain, and thus the tetragonal distortion, in the films is found to be surprisingly stable, showing less than 10% strain relief for 80 ML Co films.

• Received 2 May 2005

DOI:https://doi.org/10.1103/PhysRevB.72.155409