As the third fundamental class of collinear magnets, altermagnets have recently attracted significant interest for their potential spintronic applications. However, realizing two-dimensional (2D) altermagnets with pure spin current remains a critical challenge. In this work, taking the experimentally established $d$-wave altermagnet semiconductor α-MnTe as an example, we demonstrate that the (110)-oriented MnTe ultrathin film (${\mathrm{Mn}}_{10}{\mathrm{Te}}_{10}$) with a thickness of two unit cells is the thinnest 2D altermagnet derived from bulk MnTe along the (110) orientation, as confirmed by magnetic symmetry analysis and first-principles calculations. The resulting 2D ${\mathrm{Mn}}_{10}{\mathrm{Te}}_{10}$ ultrathin film exhibits robust dynamical stability, a low exfoliation energy of $51.3\mathrm{MeV}/{\AA }^2$, a high Néel temperature of 454 K, a large spin splitting of 492 meV, a band gap of 1.079 eV, and anomalous Hall conductivity of 95 S/cm. We further propose lattice-matched CdTe (001) as a suitable substrate for ${\mathrm{Mn}}_{10}{\mathrm{Te}}_{10}$ growth and demonstrate that interfacial strain combined with charge transfer can drive a transition from an altermagnetic semiconductor to a fully compensated ferrimagnetic half metal, thereby enabling highly spin-polarized current generation. Finally, we constructed a ${\mathrm{Mn}}_{10}{\mathrm{Te}}_{10}$/CdTe (001) magnetic tunnel junction (MTJ) and investigate its spin-resolved transport properties. At equilibrium (zero temperature, zero bias), the spin-up conductance is 44.82 µS, while the spin-down conductance is 0.23 µS, corresponding to nearly 100% spin polarization and typical half-metallic MTJ behavior. These findings highlight a viable strategy for designing 2D altermagnets in related material systems and substrate engineering as a promising strategy for developing low-power spintronic devices based on 2D altermagnets.

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• Altermagnetism
• Magnetic anisotropy
• Surface & interfacial phenomena