Stress effects on the ESR spectra of Dy in Ag thin films

ESR experiments on dilute Ag: Dy thin films at liquid-helium temperatures allow the estimation of lower limits for the second-order orbit-lattice coupling parameters. The anisotropy observed on the $g$ value of the ${\Gamma }_7$ ground state of Dy is interpreted in terms of admixtures of excited crystal-field levels with the ground state, via a planar strain of the film, induced by the difference in the thermal-expansion coefficients between the film and the substrate. The results indicate that the tetragonal orbit-lattice parameter agrees in sign with that predicted by the point-charge model, but the trigonal one does not, similar to Ag: Er thin films.