Applied-field magnetic structure and spectroscopy shifts of the effective spin-1/2 𝑋⁢𝑌-like magnet Li2⁢CoCl4

Insulators containing chains of magnetic transition metal cations provide platforms for probing spin-1/2 dynamics and quantum critical behavior. Li2⁢CoCl4 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 𝑋⁢𝑌-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.