Magnetic properties of PrPd$_{2}$Si$_{2}$ and PrPt$_{2}$Si$_{2}$

We have investigated the two rare-earth intermetallic compounds PrPd$_{2}$Si$_{2}$ and PrPt$_{2}$Si$_{2}$ by means of magnetization, electrical resistivity and heat capacity measurements. While PrPd$_{2}$Si$_{2}$ exhibits an antiferromagnetic ordering at 3 K, no magnetic ordering is observed in PrPt$_{2}$Si$_{2}$ down to 2 K. The different magnetic behaviors of these two compounnds are due to different crystalline electric field (CEF) level schemes. The specific heat data suggest a quasi-quartet ground state in PrPd$_2$Si$_2$ in contrast to a nonmagnetic singlet ground state in PrPt$_2$Si$_2$. This difference is attributed to the loss of a mirror plane upon changing the crystal structure from the ThCr$_2$Si$_2$ type (PrPd$_2$Si$_2$) to the CaBe$_2$Ge$_2$ type (PrPt$_2$Si$_2$). Further on, a large magnetoresistance is also observed in the magnetically ordered state of PrPd$_2$Si$_2$.