Valence fluctuation in Ce$_{2}$Co$_{3}$Ge$_{5}$ and crystal field effect in Pr$_{2}$Co$_{3}$Ge$_{5}$

TL;DR

This study investigates the magnetic and electronic properties of ternary rare earth germanides R₂Co₃Ge₅, revealing valence fluctuation in Ce and crystal field effects in Pr through various measurements.

Contribution

It provides new insights into valence fluctuation in Ce₂Co₃Ge₅ and crystal field effects in Pr₂Co₃Ge₅ using comprehensive experimental techniques.

Findings

Ce₂Co₃Ge₅ shows valence fluctuation with non-trivalent Ce ions.

Pr₂Co₃Ge₅ exhibits a Schottky anomaly indicating crystal field splitting.

No magnetic or superconducting transition observed down to 2 K.

Abstract

Polycrystalline samples of ternary rare earth germanides R$_{2}$Co$_{3}$Ge$_{5}$(R = La, Ce and Pr) have been prepared and investigated by means of magnetic susceptibility, isothermal magnetization, electrical resistivity and specific heat measurements. All these compounds crystallize in orthorhombic U$_{2}$Co$_{3}$Si$_{5}$ structure (space group \textit{Ibam}). No evidence of magnetic or superconducting transition is observed in any of these compounds down to 2 K. The unit cell volume of Ce$_{2}$Co$_{3}$Ge$_{5}$ deviates from the expected lanthanide contraction, indicating non trivalent state of Ce ions in this compound. The reduced value of effective moment ($\mu_{eff}$ $\approx$ 0.95 $\mu_{B}$) compared to that expected for trivalent Ce ions further supports valence fluctuating nature of Ce in Ce$_{2}$Co$_{3}$Ge$_{5}$. The observed temperature dependence of magnetic susceptibility is consistent with ionic interconfiguration fluctuation (ICF) model. Although no sharp anomaly due to a phase transition is seen, a broad Schottky-type anomaly is observed in the magnetic part of specific heat of Pr$_{2}$Co$_{3}$Ge$_{5}$. An analysis of $C_{mag}$ data suggests a singlet ground state in Pr$_{2}$Co$_{3}$Ge$_{5}$ separated from the singlet first excited state by 22 K and a doublet second excited state at 73 K.