First principles study of magneto-optical properties of half metallic Heusler alloys: NiMnSb and PtMnSb

Within the local spin density approximation (LSDA) of density functional theory, calculations of both the diagonal and off-diagonal conductivity of NiMnSb and PtMnSb are presented. The similar electronic structures of these two materials yield similar diagonal conductivities while the larger spin-orbit coupling of Pt than that of Ni results in a larger off-diagonal conductivity for PtMnSb than for NiMnSb. As a result, a larger Kerr rotation for PtMnSb is found. Quantitatively we found fair agreement between the theoretical and the experimental MOKE spectra. The discrepancy between the theory and the experiment in some details, particularly in the case of PtMnSb, is attributed to the inaccuracy in theory to give the correct plasma resonant edge, hence suggesting that a more accurate description of the energy bands such as including quasiparticle self energy corrections is required