Suppression of ferromagnetism governed by a critical lattice parameter in CeTiGe3 with hydrostatic pressure or V substitution

We combine structural and magnetic measurements to compare the different magnetic phase diagrams between the pressure and substitution studies in ${\mathrm{CeTiGe}}_{3}$. We report on the structural, magnetic, and electrical transport properties of single crystals of ${\mathrm{CeTi}}_{1\ensuremath{-}x}{\mathrm{V}}_{x}{\mathrm{Ge}}_{3}$ ($x=0$, 0.1, 0.2, 0.3, 0.4, 0.9, and 1), and of polycrystalline samples ($x=0.5$, 0.6, 0.7, 0.8), as well as structural properties of ${\mathrm{CeTiGe}}_{3}$ under pressure up to $9\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. The ferromagnetic ordering in ${\mathrm{CeTiGe}}_{3}$ is suppressed with V doping in ${\mathrm{CeTi}}_{1\ensuremath{-}x}{\mathrm{V}}_{x}{\mathrm{Ge}}_{3}$, and suggests a possible ferromagnetic quantum critical point near $x=0.45$. We perform a detailed crystalline electric field (CEF) analysis, and the magnetic susceptibility data in pure ${\mathrm{CeTiGe}}_{3}$ and ${\mathrm{CeVGe}}_{3}$ can be well explained by the CEF model. The proposed CEF energy levels suggest that there is a gradual change of the ground state from $|\ifmmode\pm\else\textpm\fi{}5/2\ensuremath{\rangle}$ in ${\mathrm{CeTiGe}}_{3}$ to $|\ifmmode\pm\else\textpm\fi{}1/2\ensuremath{\rangle}$ in ${\mathrm{CeVGe}}_{3}$, and a suppression of CEF splitting energies near the quantum critical region. When hydrostatic pressure is used instead of chemical substitution, the quantum critical point is avoided by the appearance of magnetic phases above around $4.1\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. In the substitution study, the ferromagnetic and antiferromagnetic regions are well separated, whereas they touch in the pressure study. We observe a different trend in the temperature dependence of the resistivity maximum in both studies, suggesting that the CEF splitting energy is suppressed by V substitution but enhanced by pressure. We also observe different responses in lattice constants between the two studies, highlighting the fact that substitution effects cannot be reduced to chemical pressure effects only. Nevertheless, when the magnetic phase diagrams of both hydrostatic pressure and substitution are compared, we find a common critical lattice constant $c=5.78\phantom{\rule{0.16em}{0ex}}\AA{}$ where the ferromagnetic ordering is suppressed in both studies.