Muon spin relaxation studies of magnetic order in ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{U}}_{\mathit{x}}$${\mathrm{Pd}}_3$ and ${\mathrm{UPd}}_4$

We have performed muon spin relaxation (μSR) measurements of polycrystalline specimens of ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{U}}_{\mathit{x}}$ ${\mathrm{Pd}}_3$ with x=0.1, 0.2, 0.4, and ${\mathrm{UPd}}_4$. We demonstrate that ${\mathrm{UPd}}_4$ and ${\mathrm{Y}}_{0.6}$ ${\mathrm{U}}_{0.4}$ ${\mathrm{Pd}}_3$ exhibit spin glass order, while the predominant volume fraction remains nonmagnetic at T→0 in ${\mathrm{Y}}_{0.8}$ ${\mathrm{U}}_{0.2}$ ${\mathrm{Pd}}_3$ and the muon spin relaxation rate becomes even smaller in ${\mathrm{Y}}_{0.9}$ ${\mathrm{U}}_{0.1}$ ${\mathrm{Pd}}_3$, indicating the disappearance of magnetic order with decreasing U concentration x. These results are discussed in terms of the competition between the crystalline electric field splitting ${\mathrm{\Delta }}_{\mathrm{CEF}}$ and the exchange coupling J.