Spin-phonon coupling in hexagonal Sr0.6Ba0.4MnO3

•Hexagonal Sr0.6Ba0.4MnO3 (SBMO) reveals two antiferromagnetic transitions.•Structural symmetry is maintained across the transition temperatures (TN).•Anomalous behavior of Mn displacement E1g mode position across TN values.•Non-magnetic oxygen does not show such anomaly.•The spin-phonon coupling parameter is evaluated to be 2.2cm−1. We have probed the magnetic properties of hexagonal Sr0.6Ba0.4MnO3 (SBMO) and its correlations with the vibrational spectra. Magnetization measurements reveal two antiferromagnetic transitions at 325K and at 227K. Temperature dependent Raman spectra of SBMO suggest that though structural symmetry is maintained across the transition temperatures, imprints of these magnetic transitions are noticed in anomalous behavior of Mn displacement E1g mode position in the same temperature range. A1g mode related to non-magnetic oxygen ion does not show such anomaly and follows an anharmonic behavior. Deviation from the anharmonic behavior of the E1g mode and its absence in A1g highlight the spin-phonon coupling in SBMO. The spin-phonon coupling parameter is evaluated to be 2.2cm−1.