Raman spectral weight redistribution driven by spin–lattice coupling in Sm2Ir2O7

• Raman spectra of Sm 2 Ir 2 O 7 pyrochlore reveal new magnon modes below T N ≈118 K. • 2D-COS proves the E g phonon persists but is masked by an emergent T 2g mode. • Spin–lattice coupling drives a clear spectral weight redistribution. • Spectral weight redistribution rules out a structural phase transition. The low-temperature phase transitions of the pyrochlore iridate Sm 2 Ir 2 O 7 are investigated using temperature-dependent Raman scattering. Below the magnetic transition temperature (T N ≈118 K), which we confirmed via ZFC-FC magnetic susceptibility, the Raman spectra show a striking evolution: several new magnetic features (M-peaks) emerge while the E g phonon mode at 350 cm −1 seemingly disappears. However, by applying Two-Dimensional Correlation Spectroscopy, we find that the E g mode does not actually vanish; it persists down to 10 K but becomes masked by an overlapping T 2g mode. The simultaneous damping of the E g phonon and the growth of magnon excitations point to a pronounced spectral weight redistribution driven by strong spin–lattice coupling. Our results indicate that these spectral anomalies are rooted in the intrinsic spin dynamics of the All-In-All-Out magnetic phase, rather than a structural phase transition. These findings provide a clear spectroscopic signature of how lattice and spin degrees of freedom interact in 5 d transition metal oxides.