Valence fluctuation in Ce2Co3Ge5 and crystal field effect in Pr2Co3Ge5

Polycrystalline samples of ternary rare-earth germanides R2Co3Ge5 (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 U2Co3Si5 structure (space group Ibam). No evidence of magnetic or superconducting transition is observed in any of these compounds down to 2 K. The unit cell volume of Ce2Co3Ge5 deviates from the expected lanthanide contraction, indicating non trivalent state of Ce ions in this compound. The reduced value of effective moment (μeff≈0.95 μB) compared to that expected for trivalent Ce ions further supports valence-fluctuating nature of Ce in Ce2Co3Ge5. The observed temperature dependence of magnetic susceptibility is consistent with the 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 Pr2Co3Ge5. An analysis of Cmag data suggests a singlet ground state in Pr2Co3Ge5 separated from the singlet first excited state by 22 K and a doublet second excited state at 73 K.