Exploring Low-Dimensional Magnetism in Cobalt Vanadates, $A$CoV${}_2$O${}_7$~($A$~=~Ca, Sr) : Crystal Growth and Magnetic Properties of Effective Spin-1/2 Zigzag Chains

We report the successful growth of high-quality single crystals of \ACVO, a quasi-one-dimensional zigzag chain compound containing Co${}^{2+}$ ions, using the optical floating zone method. The crystal growth was stabilized under high-pressure argon-oxygen gas with slow growth rates, overcoming challenges associated with the incongruent melting behavior of this material. X-ray diffraction confirms the zigzag arrangement of Co${}^{2+}$ ions, forming a quasi-one-dimensional chain structure. Magnetic susceptibility and heat capacity measurements reveal an antiferromagnetic phase transition at the Néel temperature ($T_{\text{N}}\sim 3.5$ K) and negative Curie-Weiss temperatures, indicative of dominant antiferromagnetic interactions. The distorted CoO${}_6$ octahedral geometry and strong spin-orbit coupling suggest that Co${}^{2+}$ ions likely exhibit an effective $J=1\mathrm{/}2$ Kramers doublet state. The results presented here demonstrate the potential of \ACVO\ as a platform for investigating low-dimensional magnetism and quantum magnetic phenomena. These insights shed light on the role of the $A$-site ion in tuning the magnetic interactions, which will foster future research into the field-induced behavior in these cobalt vanadates.