The antiferromagnets with the time-reversal symmetry broken magnetic structures possess a finite spin splitting in the momentum space, and may contribute to a realization of a finite tunnel magnetoresistance (TMR) effect even with magnets with zero net spin polarization. In this paper, we study the TMR effect with the noncollinear antiferromagnet ${\mathrm{Mn}}_3\mathrm{Sn}$ whose inverse ${120}^{\circ }$ antiferromagnetic order breaks the time-reversal symmetry. In particular, we employ the representative barrier material $\mathrm{MgO}$ as the tunnel insulator, and calculate the TMR effect in the ${\mathrm{Mn}}_3\mathrm{Sn}\left(01\overline{1}0\right)/\mathrm{MgO}\left(110\right)/{\mathrm{Mn}}_3\mathrm{Sn}$ magnetic tunnel junctions (MTJs), which has an optimal geometry for the spin-orbit torque switching of the magnetic configurations. We show that a finite TMR ratio reaching $\gtrsim 1000\%$ appears in the ${\mathrm{Mn}}_3\mathrm{Sn}/\mathrm{MgO}/{\mathrm{Mn}}_3\mathrm{Sn}$ MTJs, which is due to the spin splitting properties of ${\mathrm{Mn}}_3\mathrm{Sn}$ in the momentum space combined with the screening effect of $\mathrm{MgO}$.

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• Magnetism
• Magnetotransport
• Spintronics
• Magnetic tunnel junctions
• First-principles calculations