Inelastic Neutron Scattering study to explore Gapless Excitations in a New S = 5/2 Sawtooth Spin Chain with Strong Geometric Frustration

CaFe2O(PO4)2 (CFPO) is a rare example of a well-isolated S = 5/2 sawtooth spin chain built from corner-sharing Fe3+ triangles, combining strong geometric frustration and one-dimensionality. Magnetic susceptibility yields Curie Temperature = 1073 K and a large frustration parameter f = 70. Heat capacity and NMR study reveal three successive low-temperature magnetic transitions (15.5, 10.4, and 7.8 K), a broad Knight shift maximum, persistent spin dynamics, and strong short-range correlations. Despite a coupling ratio Jbb/Jvb=0.61 which predicts a singlet ground state for S = 1/2 analogs, CFPO exhibits gapless excitations. Interestingly CFPO also shows evidence of Magneto-Dielectric(MD) coupling.Inelastic neutron scattering (INS) on such spin chain system at MARI will allow direct mapping of the spin excitation spectrum over a wide Q E range, enabling extraction of exchange constants, identification of dispersion features, and detection of possible excitation continua from frustration. INS can also reveal MD coupling through linewidths, energy shifts, and Q-dependent intensity variations, clarifying how geometric frustration and S = 5/2 spin size conspire to produce the extended cooperative paramagnetic regime observed in CFPO.