Intrinsic properties of stoichiometric LaFePO

Abstract

DC and ac magnetization, resistivity, specific-heat, and neutron-diffraction data reveal that stoichiometric LaFePO is metallic and non-superconducting above $T=0.35\text{ }\text{K}$, with $\ensuremath{\gamma}=12.5\frac{\text{mJ}}{\text{mol}\text{ }{\text{K}}^{2}}$. Neutron-diffraction data at room temperature and $T=10\text{ }\text{K}$ are well described by the stoichiometric, tetragonal ZrCuSiAs structure, and show no signs of structural distortions or long-range magnetic ordering to an estimated detectability limit of $0.07{\ensuremath{\mu}}_{B}/\text{Fe}$. We propose a model based on the shape of the iron-pnictide tetrahedron that explains the differences between LaFePO and LaFeAsO, the parent compound of the recently discovered high-Tc oxyarsenides, which, in contrast, shows both structural and spin-density wave transitions.