Magnetic and nonmagnetic Ce in the borocarbides

We have measured the magnetic susceptibility, resistivity, and heat capacity of a series of Ce-based intermetallics CeCo₂{B}₂$C, ${CeNi}₂B₂C, CeRh₂{B}₂$C, ${CePd}₂B₂C, and CePt1.5{Au}0.5B₂C. The Ce ion changes from magnetic to nonmagnetic behavior with decreasing metal d-ion size. In the large limit, trivalent CePt1.5{Au}0.5B₂C is a single-ion Kondo system with a strongly pressure-dependent coherence temperature, Tcoh{~}30 to 100 K. CeCo₂{B}₂$C and ${CeRh}₂B₂C are both intermediate valent, the latter with a Sommerfeld constant {γ} of 75(5) mJ/mole K². CePd₂{B}₂C is primarily nonmagnetic with a small temperature-independent Pauli susceptibility of 5(1)×{10}^{{{-}}6}$ emu/mole Ce. Finally, the smallest transition-metal material, nonmagnetic ${CeNi}₂B₂{C}₂$, has properties reminiscent of the non-Ce-based borocarbides.