Magnetic order in ${\text{Pr}}_2{\text{Pd}}_3{\text{Ge}}_5$ and possible heavy-fermion behavior in ${\text{Pr}}_2{\text{Rh}}_3{\text{Ge}}_5$

We report our results on two ternary intermetallic compounds ${\text{Pr}}_2{\text{Pd}}_3{\text{Ge}}_5$ and ${\text{Pr}}_2{\text{Rh}}_3{\text{Ge}}_5$ based on magnetic susceptibility, magnetization, specific heat, resistivity, and magnetoresistance data. These compounds form in ${\text{U}}_2{\text{Co}}_3{\text{Si}}_5$-type orthorhombic structure (space group Ibam). ${\text{Pr}}_2{\text{Pd}}_3{\text{Ge}}_5$ exhibits two magnetic transitions at $T_{N1}=7.5\text{K}$ and $T_{N2}=8.3\text{K}$. In the magnetically ordered state, ${\text{Pr}}_2{\text{Pd}}_3{\text{Ge}}_5$ exhibits a field-induced metamagnetic transition and unusually large magnetoresistance. ${\text{Pr}}_2{\text{Rh}}_3{\text{Ge}}_5$ does not show any phase transition down to 0.5 K. It has a crystal electric field singlet ground state, separated from the first excited state by about 10 K. The low lying crystal field excitations lead to exciton mediated electronic mass enhancement, as evidenced by a large Sommerfeld coefficient $\left(\gamma \sim 80\text{mJ}/\text{mol}{\text{K}}^2\right)$ in ${\text{Pr}}_2{\text{Rh}}_3{\text{Ge}}_5$.

Figure 1

The temperature dependence of magnetic susceptibility of ${\text{Pr}}_2{\text{Pd}}_3{\text{Ge}}_5$ at 1.0 T. The solid line represents the fit to the modified Curie–Weiss behavior. The inset shows the low temperature magnetic susceptibility data at two different fields.

Figure 2

Isothermal magnetization of ${\text{Pr}}_2{\text{Pd}}_3{\text{Ge}}_5$ as a function of field at temperatures of 2 and 10 K.

Figure 3

Magnetic part of the specific heat of ${\text{Pr}}_2{\text{Pd}}_3{\text{Ge}}_5$. The solid line represents the fit to the three level CEF scheme, as described in the text. The inset shows the magnetic contribution to the entropy as a function of temperature.

Figure 4

Normalized electrical resistivity of ${\text{La}}_2{\text{Pd}}_3{\text{Ge}}_5$ and ${\text{Pr}}_2{\text{Pd}}_3{\text{Ge}}_5$ as a function of temperature in the temperature range 2–300 K. The upper inset shows the low temperature resistivity of ${\text{Pr}}_2{\text{Pd}}_3{\text{Ge}}_5$ at different fields, and the lower inset shows the magnetoresistance at 2 and 15 K. The solid line in the upper inset represents the fit to gapped magnon behavior in the ordered state.

Figure 5

Temperature dependence of magnetic susceptibility of ${\text{Pr}}_2{\text{Rh}}_3{\text{Ge}}_5$ at 0.1 T. The solid line represents the fit to the modified Curie–Weiss behavior. The inset shows the field dependence of isothermal magnetization at 2 K.

Figure 6

Temperature dependence of the specific heat of ${\text{La}}_2{\text{Rh}}_3{\text{Ge}}_5$ and ${\text{Pr}}_2{\text{Rh}}_3{\text{Ge}}_5$ in the temperature range 0.5–50 K. The solid line is the fit to the CEF scheme, as described in the text. The inset shows the magnetic part of the specific heat and entropy as a function of temperature. The data shown by stars in the inset represent the magnetic part to the fit in CEF analysis.

Figure 7

Normalized electrical resistivity of ${\text{La}}_2{\text{Rh}}_3{\text{Ge}}_5$ and ${\text{Pr}}_2{\text{Rh}}_3{\text{Ge}}_5$ as a function of temperature in the temperature range 2–300 K.