| Achoimre: | <p>La<sub><em>x</em></sub>Sr<sub>2–<em>x</em></sub>NiRuO<sub>6</sub>, La<sub><em>x</em></sub>Sr<sub>4–<em>x</em></sub>NiRuO<sub>8</sub>, and La<sub><em>x</em></sub>Sr<sub>3–<em>x</em></sub>NiRuO<sub>7</sub> are, respectively, the <em>n</em> = ∞, 1, and 2 members of the (La<sub><em>x</em>/2</sub>Sr<sub>1–(<em>x</em>/2)</sub>)<sub><em>n</em></sub>Sr(Ni<sub>0.5</sub>Ru<sub>0.5</sub>)<sub><em>n</em></sub>O<sub>3<em>n</em>+1</sub> compositional series. Reaction with CaH<sub>2</sub>, in the case of the La<em><sub>x</sub></em>Sr<sub>2–<em>x</em></sub>NiRuO<sub>6</sub> perovskite phases, or Zr oxygen getters in the case of the La<em><sub>x</sub></em>Sr<sub>4–<em>x</em></sub>NiRuO<sub>8</sub> and La<em><sub>x</sub></em>Sr<sub>3–<em>x</em></sub>NiRuO<sub>7</sub> Ruddlesden–Popper phases, yields the corresponding topochemically reduced (La<sub><em>x</em>/2</sub>Sr<sub>1–(<em>x</em>/2)</sub>)<sub><em>n</em></sub>Sr(Ni<sub>0.5</sub>Ru<sub>0.5</sub>)<sub><em>n</em></sub>O<sub>3<em>n</em>–1</sub> compounds (La<sub><em>x</em></sub>Sr<sub>2–<em>x</em></sub>NiRuO<sub>4</sub>, La<sub><em>x</em></sub>Sr<sub>4–<em>x</em></sub>NiRuO<sub>6</sub>, and La<sub><em>x</em></sub>Sr<sub>3–<em>x</em></sub>NiRuO<sub>5</sub>), which contain Ni and Ru cations in square-planar coordination sites. The <em>x</em> = 1 members of each series (LaSrNiRuO<sub>4</sub>, LaSr<sub>3</sub>NiRuO<sub>6</sub>, and LaSr<sub>2</sub>NiRuO<sub>5</sub>) exhibit insulating ferromagnetic behavior at low temperature, attributable to exchange couplings between the Ni<sup>1+</sup> and Ru<sup>2+</sup> centers they contain. Increasing the La<sup>3+</sup> concentration (<em>x</em> > 1) leads to a reduction of some of the Ru<sup>2+</sup> centers to Ru<sup>1+</sup> centers and a suppression of the ferromagnetic state (lower <em>T</em><sub>c</sub>, reduced saturated ferromagnet moment). In contrast, increasing the Sr<sup>2+</sup> concentration (<em>x</em> < 1) oxidizes some of the Ru<sup>2+</sup> centers to Ru<sup>3+</sup> centers and enhances the ferromagnetic coupling (increased <em>T</em><sub>c</sub>, increased saturated ferromagnet moment) for the <em>n</em> = ∞ and <em>n</em> = 2 samples but appears to have no influence on the magnetic ordering temperature of the <em>n</em> = 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.</p>
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