Computationally based explanation of the peculiar magneto-optical properties of PtMnSb and related ternary compounds

The magneto-optical (MO) spectra of 15 ternary ferromagnetic compounds are investigated on the basis of local-density band-structure calculations. The key material of interest in this study is PtMnSb, for which the MO Kerr spectra are unusually large and quite different from that of, e.g., the isoelectronic compounds NiMnSb and PdMnSb. First we show that the spectral differences between NiMnSb, PdMnSb, and PtMnSb can be fully understood from their relativistic electronic structure. Further, we investigate the following ternary ferromagnetic compounds: PtMnSn, PtCrSb, PtFeSb, Pt${}_2$MnSb, Co${}_2$HfSn, NiMnAs, PdMnAs, PtMnAs, RuMnAs, PtMnBi, BiMnPt, and PtGdBi. Within the total group of alloys, we study the MO spectra of PtMnSb in relationship to the spin-orbit coupling strength; the magnitude of the $3d$-magnetic moment; the degree of hybridization in the bonding; the half-metallic character, or, equivalently, the Fermi-level filling of the band structure; the intraband plasma frequency; and the influence of the crystal structure. We find that these characteristics form a unique combination in PtMnSb leading to its outstanding MO Kerr spectra. None of the other compounds can match up to PtMnSb in this respect. For the compounds NiMnAs, PdMnAs, PtMnAs, and, particularly, RuMnAs, whose MO spectra are not measured as yet, we predict Kerr spectra which look promising for ultraviolet laser light recording applications.