Double perovskites containing $4d\text{−}4f$ interactions provide a platform to study complex magnetic phenomena in correlated systems. Here, we investigate the magnetic ground state and quasiparticle excitations of the fascinating double perovskite system ${\mathrm{Ba}}_2{\mathrm{DyRuO}}_6$ through Time of flight (TOF) neutron diffraction, inelastic neutron scattering (INS), and theoretical modeling. The compound ${\mathrm{Ba}}_2{\mathrm{DyRuO}}_6$ is reported to exhibit a single magnetic transition, in sharp contrast with most of the other rare-earth (R) members in this family, $A_2{R\mathrm{RuO}}_6$ (A = Ca, Sr, Ba), which typically show magnetic ordering of the Ru ions, followed by R-ion ordering. Our neutron-diffraction results confirm that long-range antiferromagnetic order emerges at $T_{\mathrm{N}}\approx 47\mathrm{K}$, primarily driven by $4d\text{−}4f$ ${\mathrm{Ru}}^{5+}\text{−}{\mathrm{Dy}}^{3+}$ exchange interactions, where both Dy and Ru moments contribute to the ordered state. The ordered ground state is a collinear antiferromagnet with Ising character, carrying ordered moments of ${\mu }_{\mathrm{Ru}}=1.6\left(1\right){\mu }_{\mathrm{B}}$ and ${\mu }_{\mathrm{Dy}}=5.1\left(1\right){\mu }_{\mathrm{B}}$ at 1.5 K. Low-temperature INS reveals well-defined magnon excitations below 10 meV. SpinW modeling of the INS spectra evinces complex exchange interactions and the presence of magnetic anisotropy, which governs the Ising ground state and accounts for the observed magnon spectrum. Combined INS and Raman spectroscopy reveal crystal-electric-field (CEF) excitations of ${\mathrm{Dy}}^{3+}$ at 46.5 and 71.8 meV in the paramagnetic region. The observed CEF levels are modeled through point-charge CEF calculations, consistent with the $O_h$ site symmetry of ${\mathrm{Dy}}^{3+}$. A complementary machine-learning approach is used to calculate and analyze the phonon spectrum, enabling a direct comparison with the INS data. These combined experimental and theoretical results provide a comprehensive understanding of the origin of phonon and magnon quasiparticle excitations and their influence on the crystal structure and ground-state magnetism of ${\mathrm{Ba}}_2{\mathrm{DyRuO}}_6$.

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• Magnetic order
• Perovskites
• Inelastic neutron scattering
• Linear spin wave theory
• Machine learning
• Neutron diffraction