Experimental electronic phase diagram in a diamond-lattice antiferromagnetic system

Abstract: 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.