Spin excitations and phonons in La$_{1.5}$Sr$_{0.5}$CoO$_{4}$

Inelastic neutron scattering measurements were performed in La$_{1.5}$Sr$_{0.5}$CoO$_{4}$. At room temperature, the excitation spectrum is dominated by phonons. At low temperatures we see a mix of lattice vibrations and spin modes. By subtracting phonon contributions we are able to identify purely magnetic modes. A resonance mode was found at energies around 25-27meV, the nature of which is under investigation.