Electromagnetic properties of undoped LaFePnO (Pn P, As)

Undoped LaFePnO (Pn P, As) shows metallic resistivity and a tetragonal phase at room temperature. The electrical resistivity (ρ) of undoped LaFeAsO exhibits a sudden decrease around T_anom ∼160 K with decreasing the temperature and increases with decreasing the temperatures (T) below another threshold temperature (T_min). It makes a contrast to undoped LaFePO, which shows neither of T_anom nor T_min. The T _anom corresponds to a crystallographic phase transition: undoped LaFeAsO shows an orthorhombic phase at temperatures < 160 K. A positive magnetoresistance (MR (ρ-ρ0) / ρ0) also appears below T _anom. DFT calculations indicate that spin moment of LaFeAsO is 1.56 μ_B / Fe in an antiferromagnetic spin configuration in a tetragonal phase, while spin moment of LaFePO is almost quenched.