Research on the electrical transport properties of iron mononitrides (FeN), including ${\gamma }^{\prime \prime }\text{−}\mathrm{FeN}$ and ${\gamma }^{\prime \prime \prime }\text{−}\mathrm{FeN}$, has been hindered by difficulties in fabricating single-phase samples. In this study, nitrogen-deficient ${\gamma }^{\prime \prime }\text{−}\mathrm{FeN}$ and ${\gamma }^{\prime \prime \prime }\text{−}\mathrm{FeN}$ epitaxial films were successfully grown on ${\mathrm{Al}}_2{\mathrm{O}}_3\left(0001\right)$ substrates. Experimental characterization reveals that paramagnetic ${\gamma }^{\prime \prime }\text{−}\mathrm{FeN}$ exhibits metallic conduction, whereas antiferromagnetic ${\gamma }^{\prime \prime \prime }\text{−}\mathrm{FeN}$ behaves as a narrow-bandgap semiconductor. Remarkably, both polymorphs exhibit near-zero magnetoresistance ($\le 0.008\%$) at temperatures above 50 K, despite their distinct electronic natures. Hall effect measurements further indicate that the ordinary Hall coefficient of ${\gamma }^{\prime \prime }\text{−}\mathrm{FeN}$ undergoes a sequential sign reversal between 5 K and 400 K, whereas ${\gamma }^{\prime \prime \prime }\text{−}\mathrm{FeN}$ maintains hole-type carriers across the entire temperature range. First-principles calculations confirm that the contrasting metallic and semiconducting band structures of ${\gamma }^{\prime \prime }\text{−}\mathrm{FeN}$ and ${\gamma }^{\prime \prime \prime }\text{−}\mathrm{FeN}$, coupled with nitrogen vacancies acting as shallow electron traps, are responsible for these unique transport characteristics. This investigation provides a comparative analysis of the carrier transport behavior in FeN polymorphs, highlighting how nitrogen vacancies modulate carrier transport processes and demonstrating their intriguing immunity to magnetic-field perturbations.

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• Electrical conductivity
• Hall effect
• Magnetoresistance
• Nitrides
• Thin films
• DFT+U
• Density functional calculations
• Film deposition