  Structural, electronic, and magnetic properties of undoped and aliovalent-ion
(Ca, F)-doped LaOFeP, which undergo superconducting transitions at transition
temperatures (Tc) 4-7 K [Kamihara et al, J. Am. Chem. Soc. 128, 10012, (2006)],
were investigated. Tc of the samples varied from 2.4 to 5.5 K in the undoped
samples, and was increased up to ~7 K by Ca- and F-doping. The Tc increases are
correlated with a decrease in the lattice volume. LaOFeP exhibits paramagnetism
in the normal conducting state. Photoemission spectroscopy combined with
first-principle band calculations clarified that Fe 3d (dz2 + (dxz, dyz))
orbitals hybridized with P 3p to form a Fermi surface. The band calculations
also suggest that the 3d electron of the Fe in LaOFeP is basically in the
low-spin configuration, and that the spin moment of LaOFeP is almost quenched,
leading to the paramagnetism of the itinerant electrons.
