Investigation of magnetic ordering in the chemical substitution series CeCu$_{\mathrm{2}}$(Si$_{\mathrm{1-x}}$P$_{\mathrm{x}})_{\mathrm{2}}$

CeCu$_{\mathrm{2}}$Si$_{\mathrm{2}}$ is an exemplary correlated electron metal that features two domes of unconventional superconductivity in its temperature-pressure phase diagram. The first dome surrounds an antiferromagnetic quantum critical point, whereas the more exotic second dome may span the zero temperature termination point of a line of $f$-electron valence transitions. It has been proposed that the second superconducting dome encompasses a quantum phase transition that is associated with a Ce 4$f$-electron valence collapse, but this has yet to be established. In order to clarify this question, we recently investigated the chemical substitution series CeCu$_{\mathrm{2}}$(Si$_{\mathrm{1-}}_{x}$P$_{x})_{\mathrm{2\thinspace }}$for $x \le $ 0.1, where Si $\to $ P replacement is understood as electronic tuning. Complex magnetism and other interesting behaviors are induced, with three distinct magnetic regimes appearing with increasing $x$. Using elastic neutron scattering, we report an in-depth study of the magnetic ordering in the CeCu$_{\mathrm{2}}$(Si$_{\mathrm{1-}}_{x}$P$_{x})_{\mathrm{2}}$ series. We discuss the implications of this behavior for understanding the cerium valence, and for stabilizing remarkable behaviors throughout the Ce$T_{\mathrm{2}}X_{\mathrm{2}}$ ($T \quad =$ transition metal and$ X \quad =$ Si, Ge) family of materials.