Applied-field magnetic structure and spectroscopy shifts of the effective spin- 12 XY -like magnet Li2CoCl</mml…

Insulators containing chains of magnetic transition metal cations provide platforms for probing spin-1/2 dynamics and quantum critical behavior. Li₂CoCl₄ contains edge-sharing CoCl₆ octahedra that form chains along the crystallographic c axis and orders antiferromagnetically at zero field, but questions remain about its applied-field magnetic structure and the Co²⁺ spin state. Here, we show with neutron diffraction on a polycrystalline sample how the antialigned chains of cobalt moments begin to transition to a ferromagnetic state above 1.6 T. Further, using magnetic resonance absorption measurements and noninteracting spin models, we reveal the strongly anisotropic nature of the Co²⁺ ion's $XY$-like magnetic behavior (g_∥=2.77 and g_⊥=5.23) and its J=1/2 ground state. We therefore supply the magnetic structures and anisotropic description needed to explore the dynamics of the field-driven magnetic phases, laying the foundation for further experimental and theoretical studies.