Magneto-optical Kerr effects of half-metallic ferromagnetic transition metal chalcogenides in zinc-blende and wurtzite structures

The electronic structure and polar magneto-optical Kerr effect (MOKE) of the transition metal chalcogenides, such as CrSe, CrTe, and VTe, in zinc-blende and wurtzite structures are studied by full-potential density-functional calculations. The $p\text{−}d$ exchange interaction in these half-metallic ferromagnets is estimated and found to be ferromagnetic. The MOKE is quite large in all of these compounds. It is found that the peaks in Kerr rotation spectra lower than $3.0\mathrm{eV}$ are enhanced by the plasma resonance due to the metallic feature in the majority spin channel, while those higher than $3.0\mathrm{eV}$ originate from the quite large off-diagonal optical conductivity element. The CrTe exhibits a larger Kerr effect than the CrSe since the spin-orbit coupling of $p$ orbitals in Te is stronger than that in Se, while the larger Kerr effect in VTe than in CrTe is quite unexpected because the magnetic moment in VTe is smaller than in CrTe. This strange result is understood in terms of transitions from the underlying band structure. Our calculations can give hints to the understanding of MOKE and the design of the new materials with technologically desirable magneto-optical properties through tailoring their electronic band structures.

Figure 1

(Color online) The band structures of CrSe (upper panels), CrTe (middle panels), and VTe (lower panels) in their ZB structures, calculated without (left-hand panels) and with (right-hand panels) the spin-orbit coupling (SOC). The vertical solid and dashed lines indicate the different possible transitions from band to band. In the left-hand panels, the solid line is for band structure of the majority spin (spin-up) electrons, while the dotted line is for those of the minority spin (spin-down) ones.

Figure 2

(Color online) Calculated Kerr rotation (${\theta }_K$, solid line) and Kerr ellipticity (${\epsilon }_K$, dashed line) spectra for CrSe, CrTe, and VTe in the ZB (left panel) and WZ (right panel) structures.

Figure 3

(Color online) Separate contributions to the Kerr rotation spectra of CrSe, CrTe, and VTe in the ZB (left panel) and WZ (right panel) structures from $\mathrm{Im}\left[{\sigma }_{xy}\right]$ (solid line) and $\mathrm{Im}\left[D^{-1}\right]$ (dashed line).