Thermal and field evolution of spin dynamics in the alternating Heisenberg Jeff= 12 spin chain Sr2 Co(SeO3)3

We present a comprehensive muon spin relaxation/rotation (μSR) study of the Co2+-based alternating Heisenberg Jeff=12 spin chain system Sr2Co(SeO3)3. Low-temperature magnetic property measurements confirm a spin-singlet ground state and identify two critical fields, HC1 and HC2. At HC1, the system evolves from the spin-singlet state to a canted antiferromagnetic phase, which persists up to HC2, where the system enters a fully polarized state. This magnetically ordered phase exists between μ0HC1c=2 T and μ0HC2c=3.05 T for μ0Hc and between μ0HC1///c=2 T and μ0HC2///c=3.6 T for H//c, reflecting the presence of anisotropy. Additionally, μSR results provide insights into the thermal and field evolution of spin dynamics, revealing a thermal crossover in spin correlations, the reopening of a spin gap due to anisotropy above HC1, and the emergence of a magnon gap above HC2. These findings imply the suppressed criticality of the canted antiferromagnetic phase by anisotropy. Our study establishes Sr2Co(SeO3)3 as a model system for investigating field-driven quantum phase transitions in one-dimensional Jeff=12 quantum spin chains with anisotropy.