Large magneto-optical Kerr effect in noncollinear antiferromagnets ${\mathrm{Mn}}_{3}X(X=\mathrm{Rh},\mathrm{Ir},\mathrm{Pt})$

Magneto-optical Kerr effect, normally found in magnetic materials with nonzero magnetization such as ferromagnets and ferrimagnets, has been known for more than a century. Here, using first-principles density functional theory, we demonstrate large magneto-optical Kerr effect in high-temperature noncollinear antiferromagnets ${\mathrm{Mn}}_{3}X(X=\mathrm{Rh},\mathrm{Ir},\mathrm{Pt})$, in contrast to usual wisdom. The calculated Kerr rotation angles are large, being comparable to that of transition-metal magnets such as bcc Fe. The large Kerr rotation angles and ellipticities are found to originate from the lifting of band double degeneracy due to the absence of spatial symmetry in the ${\mathrm{Mn}}_{3}X$ noncollinear antiferromagnets which together with the time-reversal symmetry would preserve the Kramers theorem. Our results indicate that ${\mathrm{Mn}}_{3}X$ would provide a rare material platform for exploration of subtle magneto-optical phenomena in noncollinear magnetic materials without net magnetization.

Figure 1

Cubic $L{1}_2$ crystal structure of ${\mathrm{Mn}}_{3}X$ ($X=\text{Rh}$, Ir, Pt) with (a) T1 and (b) T2 spin configurations, as well as the corresponding (111) planes in (c) and (d), respectively. The red balls (each with one arrow) and green balls (without arrow) represent Mn and $X$ atoms, respectively. The dashed lines in (c) and (d) stand for the primitive cell of the kagome lattice.

Figure 2

(a) and (b) The calculated real diagonal (${\sigma }_{xx}^1$) as well as (c) and (d) imaginary off-diagonal (${\sigma }_{xy}^2$) components of the optical conductivity tensor for the T1 and T2 spin configurations of the ${\mathrm{Mn}}_{3}X$ alloys. Both ${\sigma }_{xx}^1$ and ${\sigma }_{xy}^2$ are broadened with a Lorentzian of 0.1 eV to simulate the finite lifetime effect of electron.

Figure 3

(a) and (b) The calculated imaginary diagonal (${\sigma }_{xx}^2$) as well as (c) and (d) real off-diagonal (${\sigma }_{xy}^1$) components of the optical conductivity tensor for the T1 and T2 spin configurations of the ${\mathrm{Mn}}_{3}X$ alloys. Both ${\sigma }_{xx}^2$ and ${\sigma }_{xy}^1$ are broadened with a Lorentzian of 0.1 eV.

Figure 4

The calculated complex Kerr angles for the T1 (left panels) and T2 (right panels) spin configurations of the ${\mathrm{Mn}}_{3}X$ alloys: Kerr rotations (upper panels) and Kerr ellipticities (lower panels). The arrows indicate the largest Kerr rotation angles.