Physical properties of the very heavy fermion YbCu4Ni

TL;DR

This study investigates the physical properties of the heavy fermion compound YbCu4Ni across a wide temperature range, revealing crystal field splitting, magnetic frustration, and a low-temperature Fermi-liquid-like regime.

Contribution

It provides detailed characterization of YbCu4Ni's structural, magnetic, thermal, and transport properties, highlighting its magnetic frustration and low-temperature quantum regime.

Findings

Crystal electric field levels identified at 85 K and 200 K.

Magnetic frustration observed with a regime change at 200 mK.

Fermi-liquid-like behavior with constant specific heat over temperature.

Abstract

The physical properties of the very heavy fermion YbCu$_4$Ni were characterized through structural, magnetic, thermal and transport studies along nearly four decades of temperature ranging between 50 milikelvin and 300 K. At high temperature, the crystal electric field levels splitting was determined with $\Delta_1 (\Gamma_6)= 85$ K and $\Delta_2 (\Gamma_8) \approx 200$ K, the latter being a quartet in this cubic symmetry. An effective magnetic moment $\mu_{eff} \approx 3\mu_B$ is evaluated for the $\Gamma_7$ ground state, while at high temperature the value for a Yb$^{3+}$ ion is observed. At low temperature this compounds shows the typical behavior of a magnetically frustrated system undergoing a change of regime at a characteristic temperature $T^*\approx 200$ mK into a sort of Fermi-liquid type 'plateau'of the specific heat: $C_m/T|_{T\to 0}$ = 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 from the nature of this ground state are revealed by the specific heat behavior under applied magnetic field.