Spin dynamics of the quasi-two-dimensional ferromagnetic bilayer manganite La 1.2 Sr 1.8 Mn 2 O 7

摘要: We have investigated the spin dynamics of the quasi-two-dimensional bilayer manganite La 1.2 Sr 1.8 Mn 2 O 7, which shows colossal magnetoresistance (CMR) behavior, by inelastic neutron scattering. We have taken advantage of the recently developed multiplexing technique with a three-axis spectrometer to map simultaneously a large region of the (Q, ω) space in a low-dimensional magnetic system. We have measured the spin wave dispersion at T= 16 K along [100], followed the temperature evolution of the spin wave dispersion close to T C≈ 128 K and also measured the scattered neutron intensities in the (Q, ω) space above T C up to T= 200 K. The magnetic inelastic intensity above T C looks qualitatively very similar to those below T C and have a structure in the (Q, ω) space suggesting persistent spin waves. However, although there exist well defined peaks at finite energies in constant energy slices up …