Reexamination of the Electronic Phase Diagram of Doped NiS₂: Electronic, Magnetic, and Structural Inhomogeneity across the Mott Insulator-Metal Transition

Pyrite-structure NiS₂ is a model antiferromagnetic (AF) Mott insulator that can be doped through insulator-metal transitions with both electrons (e^-) and holes (h⁺), enabling fine-tuning of electronic/magnetic properties. Despite decades of studies, the electronic/magnetic behavior of NiS₂ remains challenging to understand. Here, we completely reexamine the electronic phase behavior of e^- and h⁺ doped Ni_1-xCu_xS₂ and Ni_1-xCo_xS₂ single crystals via magnetometry, heat capacity, neutron diffraction, and electronic transport. We find that prior work overlooked vital details of the magnetic ordering in this system. While e^- and h⁺ doping rapidly increase the AF ordering temperature (T_ND) by 4-fold at as little as x ≈ 0.1, signatures of AF and weak ferromagnetic (WF) ordering remain at the same temperatures (T_N and T_wf) as undoped NiS₂. As T_N and T_wf remain constant, the associated magnetic moments diminish with doping, strongly implicating magnetic phase coexistence across the Mott insulator-metal transition, accompanied by substantial structural changes and inhomogeneity. The insulator-metal transition is also strongly e^-/h⁺ asymmetric, which we interpret via dynamical mean-field theory calculations.