Optical spectroscopy investigations of half metallic ferromagnetic Heusler alloy thin films: PtMnSb, NiMnSb, and CuMnSb

We have studied the optical properties of cosputtered XMnSb (X=Cu,Ni,Pt) thin films using light transmission, reflection, and spectroscopic ellipsometry. We observed a feature in the transmission spectra suggestive of a band gap of energy ∼1.5–1.7 eV for PtMnSb, ∼1.1 eV for NiMnSb and ∼0.8 eV for CuMnSb. This behavior is consistent with predictions of the half metallic ferromagnetic state in PtMnSb and NiMnSb. The values for PtMnSb and NiMnSb are larger than the ones previously reported by other authors on bulk polished samples. We interpret this discrepancy as due to surface contamination of the bulk samples or nonstoichiometry in our films.