We have studied the magnetic properties of pure ${\mathrm{PrAu}}_2{\mathrm{Si}}_2.$ The data show the characteristic features of a canonical spin glass with a freezing temperature of $T_F=3\mathrm{}\hspace{0.5em}\mathrm{K}.\mathrm{}$ Thus, ${\mathrm{PrAu}}_2{\mathrm{Si}}_2$ is to our knowledge the first example of a pure rare-earth spin glass with well-localized magnetic moments and without any intentionally introduced disorder. Recently, Süllow et al. [S. Süllow, G. J. Nieuwenhuys, A. A. Menowsky, J. A. Mydosh, S. A. M. Mentik, T. E. Mason, and W. J. L. Buyers, Phys. Rev. Lett. $78,$ 354 (1997)] discovered heavy-fermion spin-glass behavior in ${\mathrm{URh}}_2{\mathrm{Ge}}_2.$ Our present results reveal that ${\mathrm{URh}}_2{\mathrm{Ge}}_2$ is not a unique case and that strong hybridization of the localized moments with the band states is not a necessary ingredient but that spin-glass behavior might be a much more widespread phenomenon in ternary ${\mathrm{RT}}_2{X}_2\hspace{0.5em}(R=\mathrm{rare}\mathrm{}\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{t}\mathrm{h}/\mathrm{U},T=\mathrm{transition}\mathrm{}\mathrm{metal},X=\mathrm{S}\mathrm{i},\mathrm{}\mathrm{Ge})$ compounds. However, the origin of the frustration, which is necessary to achieve a disordered ground state, still has to be elucidated in this new class of spin-glass compounds.

• Received 18 May 1998

DOI:https://doi.org/10.1103/PhysRevB.59.R6604