Asymmetric Magnetoresistance and Ultrafast Carrier Transport in Ni-Doped MoS2 Nanosheets
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Pure and Ni doped MoS 2 (Mo 1 − x Ni x S 2 at x = 0, 2, 4, 6, and 8%) nanosheets were synthesized via hydrothermal method to study the effect of Ni on their structural, optical, morphological, and transport properties. XRD confirmed the samples having hexagonal phase, with peak shifts and disappearance of the (002) reflection at higher doping levels, indicating lattice strain and reduced crystallinity supported by Raman spectra. HR-TEM micrographs confirm the formation of nanosheets decorated with Ni quantum dots. PL spectra exhibited A and B exciton peaks at ~ 797 nm and ~ 689 nm, with Ni doping affecting exciton dynamics and non-radiative recombination. Hall measurements shows n-type conduction in all samples, with carrier concentration and mobility strongly dependent on Ni content. Low doping (2%) reduces mobility and increases resistivity, while higher doping (8%) mobility (~ 2.13×10⁵ cm²/V·s) and conductivity (0.608 S/cm) increases, induces metallic-like behavior with very high mobility. The R-T behavior of 4% Ni-doped MoS 2 a semiconductor-to-metal-like transition near 220–250 K, with resistivity decreasing exponentially with temperature in the semiconducting regime and shifting to higher resistivity under applied magnetic field, confirming field-induced suppression of carrier mobility. It demonstrates a distinctive asymmetric MR(H) hysteresis with significant positive and negative MR contributions, confirming the coexistence of orbital and spin-dependent scattering mechanisms. The asymmetry (-10.22% Vs 23.36%) strongly evidences the role of localized Ni moments and defect-induced magnetic states in modulating carrier transport.
