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 $\le x\le$ 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.

8 pages, 5 figures

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