Asymmetric magnetoresistance and enhanced carrier transport in Ni-doped MoS2 nanosheets

In this study, we report the novel observation of a doping-induced semiconductor-to-metal-like transition and asymmetric magnetoresistance (MR) in Ni-doped MoS₂ nanosheets synthesized via a hydrothermal method. Pure and Ni-doped MoS₂ (Mo_1−xNi_xS₂; x = 0, 2, 4, 6, and 8%) nanosheets were systematically investigated to elucidate the influence of Ni incorporation on their structural, optical, and transport properties. XRD confirmed a hexagonal phase with progressive peak shifts and disappearance of the (002) plane at higher doping, signifying lattice strain and reduced crystallinity, further supported by Raman analysis. HR-TEM images revealed few-layer nanosheets decorated with Ni quantum dots, validating successful doping and nanosheets morphology. Photoluminescence spectra exhibited A and B excitonic peaks at ~ 797 nm and ~ 689 nm, respectively, with Ni doping modulating exciton recombination and non-radiative pathways. Hall measurements confirmed n-type conduction in all samples, with carrier mobility and concentration strongly dependent on Ni content. Notably, 8% Ni doping resulted in an exceptionally high mobility (~ 2.13 × 10³ cm²/V s) and enhanced conductivity (6.074 × 10^–3 S/cm), signifying metallic-like transport. The 4% Ni-doped sample exhibited a semiconductor-to-metal-like transition near 220–250 K, while magnetic field-dependent R-T measurements showed field-induced suppression of mobility. Moreover, a distinctive asymmetric MR(H) hysteresis (− 10.22% vs + 23.36%) revealed the coexistence of orbital and spin-dependent scattering, confirming the influence of localized Ni moments and defect-induced magnetic states on carrier transport. These results establish Ni-doped MoS₂ as a promising platform for exploring spin-charge coupling and tunable quantum transport in layered transition-metal dichalcogenides.