${}^{27}\mathrm{Al}$ NMR measurements have been performed to investigate the ordering mechanism and spin fluctuations in a geometrically frustrated heavy-fermion antiferromagnet on the Kagome-like lattice CePdAl. This compound shows a partially ordered state below $T_{\mathrm{N}}$ $\left(2.7\mathrm{K}\right)$, in which $1∕3$ of the Ce moments remain paramagnetic. Whether the remaining paramagnetic moments order at lower temperature or not has been controversial. Our NMR measurements show that the nuclear magnetic relaxation rate $T_1^{-1}$ is proportional to the temperature below $0.2\mathrm{K}$ and there is no other phase transition down to $30\mathrm{mK}$. The simulation of the spin echo spectra shows that the observed spectra are compatible with the partially ordered state and an incommensurate $k$ vector along the $c$ axis down to the lowest temperature. These results demonstrate that the paramagnetic Ce moments in the partially ordered state are in a heavy-fermion state and consequently the partially ordered state is considered to be stable down to $0\mathrm{K}$. The temperature dependence of $T_1^{-1}$ also shows that antiferromagnetic correlations develop from much higher temperatures above $T_{\mathrm{N}}$.

• Received 1 May 2007

DOI:https://doi.org/10.1103/PhysRevB.77.064432