Electrical and magnetic properties of quaternary compounds LnMnPO (Ln = Nd, Sm, Gd) with ZrCuSiAs-type structure

Electronic and optical properties of layered compounds LnMnPO (Ln = Nd, Sm, Gd) are investigated in comparison with an antiferromagnetic semiconductor LaMnPO. Diffuse reflectance spectra and temperature dependent electrical conductivity indicate that the LnMnPO compounds are semiconductors with band gap energies of 0.7–0.8 eV. Electrical conductivity at RT is varied from 4 × 10−3 to 2.5 S cm−1 by Cu doping for NdMnPO. Nominally undoped LnMnPO compounds exhibit negative Seebeck coefficients due presumably to P deficiency, while the sign of the Seebeck coefficients is changed to positive by doping of Ca or Cu to the Ln sites, indicating that the polarity of the predominant carriers in LnMnPO is controlled by doping. Mn spins in NdMnPO are already in an antiferromagnetic ordering state below 350 K, while antiferromagnetic ordering of Nd spins occurs at ∼10 K.