Effects of Fe doping of La1.85Sr0.15CuO4

In singly doped samples of La1.85Sr0.15Cu1-xFexO4 and doubly doped samples of La1.85-xSr0.15+xCu1-xFexO4, Fe ions substitute for Cu2+ at the valence of 3+. The depression of T-c is less sharp in doubly doped samples than in singly doped samples due to the compensation of carriers. We consider that doping with Fe severely disturbs the alignment of Cu(3d(x2-y2)) and O(2p(sigma)) orbitals and leads to the formation of CuO6 clusters. The charge carriers in these CuO6 clusters lose their itineracy and show localized behaviour. The decrease in T-c caused by Fe doping is due to the localization of carriers but not to the existence of an impurity moment.