Experimental electronic phase diagram in a diamond-lattice antiferromagnetic system

We report Ni-doping effect on the magnetic and electronic properties of thiospinel Co\(_{1-x}\)Ni\(_x\)[Co\(_{0.3}\)Ir\(_{1.7}\)]S\(_4\) (0 \(\leq x \leq\) 1). The parent compound Co[Co\(_{0.3}\)Ir\(_{1.7}\)]S\(_4\) exhibits antiferromagnetic order below \(T_\mathrm{N} \sim\) 292 K within the \(A\)-site diamond sublattice, along with a narrow charge-transfer gap. Upon Ni doping, an insulator-to-metal crossover occurs at \(x \sim\) 0.35, and the antiferromagnetism is gradually suppressed, with \(T_\mathrm{N}\) decreasing to 23 K at \(x =\) 0.7. In the metallic state, a spin-glass-like transition emerges at low temperatures. The antiferromagnetic transition is completely suppressed at \(x_\mathrm{c} \sim\) 0.95, around which a non-Fermi-liquid behavior emerges, evident from the \(T^\alpha\) temperature dependence with \(\alpha \approx\) 1.2-1.3 in resistivity and divergent behavior of \(C/T\) in specific heat at low temperatures. Meanwhile, the electronic specific heat coefficient \(\gamma\) increases substantially, signifying an enhancement of the quasiparticle effective mass. The magnetic phase diagram has been established, in which an antiferromagnetic quantum critical point is avoided at \(x_\mathrm{c}\). Conversely, the observed glass-like tail above the critical concentration aligns more closely with theoretical predictions for an extended region of quantum Griffiths phase in the presence of strong disorder.