Magnetostriction of dilute AuYb and AuTb monocrystals

We have made magnetostriction measurements on dilute $\text{Au}$Yb and $\text{Au}$Tb monocrystals at low temperatures. The shape magnetostriction follows the sign of the quadrupolar Stevens factor α_J of the earth but, in contrast to our recent results on silver-rare earth dilute alloys, the 〈001〉 and 〈111〉 effects have opposite signs. We obtain very good agreement between experiment and calculations based on the known cubic crystal-field parameters and we estimate the ion-lattice coupling parameters. The volume magnetostriction is positive, but very small, about two orders of magnitude smaller than the shape effect.