Thermal and magnetic properties of La-doped $Ce1−yLayGe1.80$ with $<y<1.0$

$CeGex$ with $1.71<x⩽2.0$ crystallizes in an orthorhombic structure and exhibits two magnetic transitions: an antiferromagnetic transition at $TN=7K$ and a ferromagnetic transition at $TC=4.3K$⁠. When $x$ decreases below 1.71, $CeGex$ transforms to a tetragonal structure and exhibits only an antiferromagnetic transition at $TN=7K$⁠. We have further studied the physical properties of La-doped $Ce1−yLayGe1.80$ with $0<y<1.0$⁠. The magnetization and specific-heat measurements show that with initial La substitution for Ce, $TN$ decreases monotonically while $TC$ increases slightly, and $TN$ and $TC$ merge to become a single ferromagnetic state at $TC=4.8K$ in the vicinity of $y=0.22$⁠. With further La doping, $TC$ decreases slowly and linearly from 4.8 to 1.75 K at $y=0.65$⁠. The x-ray measurements show that the lattice parameters remain nearly unchanged in the two magnetic transition regimes with $0<y<0.22$ and increase monotonically with further La substitution for Ce $(0.22<y⩽1.0)$⁠. The entropy removal and magnetic moment calculations are also discussed.