Magnetic and nonmagnetic Ce in the borocarbides

We have measured the magnetic susceptibility, resistivity, and heat capacity of a series of Ce-based intermetallics ${\mathrm{CeCo}}_2$ ${\mathrm{B}}_2$C, ${\mathrm{CeNi}}_2$ ${\mathrm{B}}_2$C, ${\mathrm{CeRh}}_2$ ${\mathrm{B}}_2$C, ${\mathrm{CePd}}_2$ ${\mathrm{B}}_2$C, and ${\mathrm{CePt}}_{1.5}$ ${\mathrm{Au}}_{0.5}$ ${\mathrm{B}}_2$C. The Ce ion changes from magnetic to nonmagnetic behavior with decreasing metal d-ion size. In the large limit, trivalent ${\mathrm{CePt}}_{1.5}$ ${\mathrm{Au}}_{0.5}$ ${\mathrm{B}}_2$C is a single-ion Kondo system with a strongly pressure-dependent coherence temperature, ${\mathit{T}}_{\mathrm{coh}}$∼30 to 100 K. ${\mathrm{CeCo}}_2$ ${\mathrm{B}}_2$C and ${\mathrm{CeRh}}_2$ ${\mathrm{B}}_2$C are both intermediate valent, the latter with a Sommerfeld constant γ of 75(5) mJ/mole ${\mathrm{K}}^2$. ${\mathrm{CePd}}_2$ ${\mathrm{B}}_2$C is primarily nonmagnetic with a small temperature-independent Pauli susceptibility of 5(1)×${10}^{\mathrm{-}6}$ emu/mole Ce. Finally, the smallest transition-metal material, nonmagnetic ${\mathrm{CeNi}}_2$ ${\mathrm{B}}_2$ ${\mathrm{C}}_2$, has properties reminiscent of the non-Ce-based borocarbides.