Anomalous spin dynamics and excitations of the quasizigzag chain compound AgCr P2 S6

We investigate the spin dynamics and low-energy magnetic excitations of an S = 3/2 spin zigzag chain system in the van der Waals material AgCrP2S6 using electron spin resonance (ESR) and Raman spectroscopy. The temperature-dependent resonance intensity and g factor reveal the development of critical correlations as the temperature approaches the ordering temperature. Additionally, the temperature-dependent linewidth of the magnetic resonance exhibits power-law behavior, characteristic of low-dimensional spin systems. The twofold angular dependence of the ESR linewidth and the significant magnetic Raman scattering in interchain (bb) polarization suggests coupling between the zigzag Cr3+ chains. Furthermore, anomalies in the ESR parameters and the Fano mode observed in Raman data around T∗ ≈ 120 K, together with an order-parameter-like shift of the magnetic spectral weight toward T∗, indicate a change in the nature of the underlying magnetic excitations, induced by non-negligible next-nearest neighbor interactions and interchain couplings, which become effective below T∗.