The magneto-optical polar Kerr effect of L10(CuAu)-type ordered alloys TM-X (TM = Mn, Fe, Co; X = Pt, Au) was calculated from the electronic structures given by the first-principles LMTO-ASA method. The calculated results agreed reasonably well with the experimental results. The important optical transitions were identified by detailed analysis of the electronic structures and transition matrix elements. As an example, it was found that the peak structure at 4 eV in the Kerr spectra of L10-FeAu mainly originated from the d↓±2 → f↓±3 transitions on Au, in which the strength of the d↓-2 → f↓-3 transition was much larger than the d↓+2 → f↓+3 transition due to the large spin-orbit splitting in Au(5d↓±2)-band. In this transition, the final state Au(5f↓±3) is a small tail state hybridized with the unoccupied Fe(3d↓) state. Thus, the transition can simply be described as the Au(5d↓) → Fe(3d↓) transition as predicted by Sato et al. [J. Magn. Soc. Japan 20(S1) (1996) 35]. Another type of transition p↓±1 → d↓±2 on Pt was found to be very strong and plays an important role in the Kerr spectra of TM-Pt, since there are many final states (Pt(5d↓)) in the transition due to the spin polarization in Pt(5d)-bands.
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