This work presents a comprehensive investigation of the structural, magnetic, and electronic properties of the double perovskite Ba$_2$CoMoO$_6$ (BCMO). Single crystals were grown via floating-zone and Czochralski techniques and characterized using a set of complementary methods. X-ray diffraction analysis confirmed that BCMO crystallizes in a face-centered cubic structure with space group $Fm\bar{ 3}m$. Magnetic susceptibility measurements reveal antiferromagnetic ordering below $T_\mathrm{ N} = 20.1(1)$~K, with a spin-flop transition at $\mu_0 H = 2.65$~T. Heat-capacity measurements and entropy analysis, $\Delta S \approx 0.95\,R\ln 2$, are consistent with a $J_\mathrm{ eff} = \tfrac{ 1}{ 2}$ effective ground state for Co$^{ 2+}$ ions. X-ray absorption spectroscopy at the Co~$L_{ 2,3}$ edges provides insight into the local electronic structure, revealing spin-orbit and crystal-field splitting effects; cluster-model calculations constrained by the XAS spectra yield a Land\'{ e} $g$ factor $g = 4.52$, consistent with a spin-orbit-entangled $J_\mathrm{ eff} = \tfrac{ 1}{ 2}$ ground state. Surface photovoltage spectroscopy reveals a strong optical response with a prominent feature at $2.65$~eV. These findings advance the understanding of face-centered cubic lattice antiferromagnets with strong spin-orbit coupling and suggest the technological promise of BCMO for spintronic and energy-conversion applications.
Categories: cond-mat.str-el cond-mat.mtrl-sci