Hole and Electron Doping of Topochemically Reduced Ni(I)/Ru(II) Insulating Ferromagnetic Oxides

LaxSr2–xNiRuO6, LaxSr4–xNiRuO8, and LaxSr3–xNiRuO7are, respectively, then= ∞, 1, and 2 members of the (Lax/2Sr1–(x/2))nSr(Ni0.5Ru0.5)nO3n+1compositional series. Reaction with CaH2, in the case of the LaxSr2–xNiRuO6perovskite phases, or Zr oxygen getters in the case of the LaxSr4–xNiRuO8and LaxSr3–xNiRuO7Ruddlesden–Popper phases, yields the corresponding topochemically reduced (Lax/2Sr1–(x/2))nSr(Ni0.5Ru0.5)nO3n–1compounds (LaxSr2–xNiRuO4, LaxSr4–xNiRuO6, and LaxSr3–xNiRuO5), which contain Ni and Ru cations in square-planar coordination sites. Thex= 1 members of each series (LaSrNiRuO4, LaSr3NiRuO6, and LaSr2NiRuO5) exhibit insulating ferromagnetic behavior at low temperature, attributable to exchange couplings between the Ni1+and Ru2+centers they contain. Increasing the La3+concentration (x> 1) leads to a reduction of some of the Ru2+centers to Ru1+centers and a suppression of the ferromagnetic state (lowerTc, reduced saturated ferromagnet moment). In contrast, increasing the Sr2+concentration (x< 1) oxidizes some of the Ru2+centers to Ru3+centers and enhances the ferromagnetic coupling (increasedTc, increased saturated ferromagnet moment) for then= ∞ andn= 2 samples but appears to have no influence on the magnetic ordering temperature of then= 1 samples. The magnetic couplings and influence of doping are discussed on the basis of superexchange and direct exchange couplings between the square-planar Ni and Ru centers.