Exchange and relaxation of rare-earth impurities and conduction electrons in YbAl₂:R (R=Nd, Eu, Gd, Dy, Er)

The authors use the bottleneck phenomena in YbAl₂:Gd and YbAl₂:Eu to extract the conduction electrons' spin-flip relaxation to the lattice, delta _eL^(O). The values observed are compared with those observed in the other dialuminides, XAl₂:Gd (X=Sc, Y, La, Lu). A correlation between delta _eL^(O) and the atomic number of the host X atom is clearly demonstrated, and is similar to that found by others for rare-earth beryllides. A simple model is suggested to explain this observed phenomenon. The ESSR isothermal limit of the R ion in YbAl₂ enables one to extract the dependence of the ion-conduction electron exchange coupling of the 4f occupation number. The authors' results shed some light on the nature of the Yb ions in YbAl₂ at low temperatures.