Physical properties of the magnetically frustrated very-heavy-fermion compound YbCu4Ni

The physical properties of the very-heavy-fermion compound ${\mathrm{YbCu}}₄\mathrm{Ni}$ were characterized through structural, magnetic, thermal, and transport studies along nearly four decades of temperature ranging between 50 mK and 300 K. At high temperature, the crystal electric field level splitting was determined with ${\mathrm{\ensuremath{\Delta}}}₁({\mathrm{\ensuremath{\Gamma}}}₆)=85\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${\mathrm{\ensuremath{\Delta}}}₂({\mathrm{\ensuremath{\Gamma}}}₈)\ensuremath{\approx}200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the latter being a quartet in this cubic symmetry. An effective magnetic moment ${\ensuremath{\mu}}_{\mathrm{eff}}\ensuremath{\approx}3{\ensuremath{\mu}}_B$ is evaluated for the ${\mathrm{\ensuremath{\Gamma}}}₇$ ground state, while at high temperature the value for a ${\mathrm{Yb}}³⁺$ ion is observed. At low temperature this compound shows the typical behavior of a magnetically frustrated system undergoing a change of regime at a characteristic temperature ${T}^*\ensuremath{\approx}200\phantom{\rule{0.16em}{0ex}}\mathrm{mK}$ into of Fermi-liquid-type ``plateau'' of the specific heat: ${C}_m{/T|}_{T\ensuremath{\rightarrow}0}$ = const. The change in the temperature dependence of the specific heat coincides with a maximum and a discontinuity in respective inductive and dissipative components of the ac susceptibility. More details about the nature of this ground state are revealed by the specific heat behavior under applied magnetic field.