Spin wave damping in colossal magnetoresistive La$_{0.7}$Ca$_{0.3}$MnO$_{3}$

The hole-doped perovskite La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ is best known for the colossal magnetoresistance displayed at a combined ferromagnetic and metal-insulator phase transition ($T_c$=257~K). Previous studies have reported that the spin wave excitations in the ferromagnetic phase become anomalously damped near the Brillouin zone boundary, though a later work suggested that this was a measurement artifact due to an optical phonon branch. We have used the ARCS time-of-flight neutron spectrometer to investigate the spin wave excitations of La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ at $T$=100~K and find a damping for spin waves at energies exceeding 20~meV that cannot be explained solely by proximity to the phonon branch. With additional measurements using the BT7 triple-axis neutron spectrometer, the spin wave damping is explored as a function of reduced wavevector, excitation energy, and temperature.