Magnetic Anisotropy and Spin-Order in Ir-Substituted Ba₄Ru₃O₁₀

We report a neutron diffraction study of the magnetic structure in Ir-doped Ba₄Ru₃O₁₀, a member of the Ruddlesden-Popper ruthenate series characterized by face-sharing Ru₃O₁₂ octahedral trimers. Our measurements reveal the compound adopts a zig-zag antiferromagnetic structure with a propagation vector k = (0, 0, 0). Magnetic moments of 0.85(5) μ_B per Ru⁴⁺ ion are observed only on the two Ru(2) sites, while the central Ru(1) site remains nonmagnetic. Although the overall magnetic structure and ordered moment closely resemble those of the parent Ba₄Ru₃O_10, the Ir substitution on the Ru sites reduces the Néel temperature from 105 K to 80 K, likely due to weakening of the intra-trimer Ru–Ru exchange coupling. Furthermore, Ir doping induces magnetic interaction anisotropy, as evidenced by magnetic in susceptibility measurements. This behavior is likely driven by an enhancement of the Ising character of the magnetic interactions, arising from the intrinsically Ising-like nature of the Ir ions, and results in increased anisotropy.