Evolution of magnetic and orbital properties in the magnetically diluted A -site spinel Cu1−xZnxRh2O4

In frustrated spinel antiferromagnets, dilution with nonmagnetic ions can be a powerful strategy for probing unconventional spin states or uncovering interesting phenomena. Here, we present x-ray, neutron scattering, and thermodynamic studies of the effects of magnetic dilution of the tetragonally distorted $A$-site spinel antiferromagnet, ${\mathrm{CuRh}}_{2}{\mathrm{O}}_{4}$, with nonmagnetic ${\mathrm{Zn}}^{2+}$ ions. Our data confirm the helical spin order recently identified at low temperatures in this material, and further demonstrate a systematic suppression of the associated N\'eel temperature with increasing site dilution towards a continuous transition with critical doping of ${x}_{\mathrm{spin}}\ensuremath{\sim}0.44$. Interestingly, this critical doping is demonstrably distinct from a second structural critical point at ${x}_{JT}\ensuremath{\sim}0.6$, which is consistent with the suppression of orbital order on the $A$ site through a classical percolative mechanism. This anomalously low value for ${x}_{\mathrm{spin}}$ is confirmed via multiple measurements, and is inconsistent with predictions of classical percolation theory, suggesting that the spin transition in this material is driven by an enhancement of preexisting spin fluctuations with weak dilution.