Anomalous spin dynamics in La0.9Ca0.1MnO3

Elastic and inelastic neutron scattering has been measured in La0.9Ca0.1MnO3 single crystal. The temperature dependence of the intensities of Bragg peaks (0 0 1) and (0 0 2) shows two magnetic transitions: a transition paramagnetic/ferromagnetic (F) at T-C = 138 K and a transition ferromagnetic/canted antiferromagnetic (AF) at T-N = 118 K. Moreover, spin waves connected to super exchange integrals, coupling localized spins of Mn3+ ions, have been determined. In addition to these spin waves, as already known in low doping rate compounds, new magnetic excitations have been measured. They appear as eigenmodes of the whole system and have a F character. Their intensity reveals a finite correlation length and the dispersion law is nearly isotropic (omega = omega(0) + Bq(2)). This new spin wave branch could be a precursor effect of the transition insulator/metal expected around x similar to 18%. (C) 1999 Elsevier Science B.V. All rights reserved.