Superconductivity and magnetism in noncentrosymmetric LaPtGe3 and CePtGe3

${\mathrm{LaPtGe}}_{3}$ and ${\mathrm{CePtGe}}_{3}$ crystallize with a noncentrosymmetric body-centered tetragonal (space group $I4mm$)$\phantom{\rule{4pt}{0ex}}{\mathrm{BaNiSn}}_{3}$-type of structure. ${\mathrm{LaPtGe}}_{3}$ is a weakly coupled BCS-like $s$-wave type-I superconductor with ${T}_{\mathrm{c}}=0.55$ K, ${B}_{\mathrm{c}}\ensuremath{\simeq}14$ mT, and Ginzburg-Landau parameter ${\ensuremath{\kappa}}_{\mathrm{GL}}=0.021l1/\sqrt{2}$. ${\mathrm{CePtGe}}_{3}$ is a nonsuperconducting (${T}_{\mathrm{nsc}}=0.35$ K) metal with an effective magnetic moment ${\ensuremath{\mu}}_{\mathrm{eff}}=2.46{\ensuremath{\mu}}_{\mathrm{B}}$. The Ce moments show two antiferromagnetic ordering transitions at ${T}_{\mathrm{N}1}\ensuremath{\approx}3.7$ K and ${T}_{\mathrm{N}2}\ensuremath{\approx}2.7$ K and a ground-state multiplet $J=5/2$ splitting into three doublets (energy splittings from the ground state ${\mathrm{\ensuremath{\Delta}}}_{1}=46$ K and ${\mathrm{\ensuremath{\Delta}}}_{2}=137$ K). The moderately enhanced Sommerfeld coefficient ${\ensuremath{\gamma}}_{0}$ and the observation of almost the full critical magnetic entropy at ${T}_{\mathrm{N}1}$ suggest that magnetic Ruderman-Kittel-Kasuya-Yosida-type interactions are dominant in ${\mathrm{CePtGe}}_{3}$, leading to a magnetically ordered ground state.