Evidence for random strain at the cubic site of Yb3+ in palladium by Moessbauer spectroscopy on 170Yb

We have analysed the slow relaxation Moessbauer emission spectrum obtained at T = 0.11 K of the paramagnetic ion Yb3+ in palladium. In this alloy, the two Yb3+ lowest crystal field states (ground state GAMMA7 and first excited state GAMMA8) are quasi-degenerate (separation Δ approximately equal 2.5 K). In this situation the magnetic hyperfine spectrum is very sensitive to crystal field distortions away from cubic symmetry, which gives rise to an important static broadening of the lines. Our lineshape analysis provides an estimate of the product of the magnetoelastic constant V and the mean square deviation σ of the random strain distribution: Vσ = 0.04 K. The spectrum lineshape suggests that the predominant distortions in PdYb have GAMMA5 symmetry. In addition, we put in evidence finer effects related to the hyperfine interaction when treated to second perturbation order