The ground state properties of CeFePO, a homologue of the new high temperature superconductors $R{\mathrm{FePnO}}_{1-x}{\mathrm{F}}_x$, were studied by means of susceptibility, specific heat, resistivity, and NMR measurements on polycrystals. All the results demonstrate that this compound is a magnetically nonordered heavy fermion metal with a Kondo temperature $T_K\sim 10\mathrm{K}$, a Sommerfeld coefficient $\gamma =700\mathrm{mJ}/\mathrm{mol}{\mathrm{K}}^2$, and a mass enhancement factor of the order of 50. Analysis of the susceptibility data and of the spin relaxation time indicates that the strong electronic correlation effects originate from the Ce-$4f$ electrons rather than from Fe-$3d$ electrons. An enhanced Sommerfeld-Wilson ratio $R=5.5$ as well as a Korringa product $S_0/T_{1}T{K}^2\simeq 0.065$ well below 1 indicate the presence of ferromagnetic correlations. Therefore, CeFePO appears to be on the nonmagnetic side of a ferromagnetic instability.

• Received 18 April 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.117206