Ab initio study of magnetoresistance effect in $\mathrm{Mn_{3}Sn}/\mathrm{MgO}/\mathrm{Mn_{3}Sn}$ antiferromagnetic tunnel junction

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 $\mathrm{Mn_{3}Sn}$ 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 $\mathrm{Mn_{3}Sn}(01\bar{1}0)/\mathrm{MgO}(110)/\mathrm{Mn_{3}Sn}$ 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 $\mathrm{Mn_{3}Sn}/\mathrm{MgO}/\mathrm{Mn_{3}Sn}$ MTJs, which is due to the spin splitting properties of $\mathrm{Mn_{3}Sn}$ in the momentum space combined with the screening effect of $\mathrm{MgO}$.