Magnetic coupling induced by hole doping in perovskites La1-xCaxMnO3:: A neutron scattering study

Elastic and inelastic neutron scattering has been used to study static and dynamic magnetic properties in Ca-doped LaMnO3 perovskites in the region of low doping (5% and 8%) and to determine the phase diagram. In addition to the spin-wave branch related to the superexchange coupling between Mn ions (ferromagnetic in the basal planes and antiferromagnetic along the direction perpendicular to them), a new type of ferromagnetic spin excitation branch is found induced by hole doping. This is revealed by well-defined propagative spin wave modes with a gap and a nearly isotropic dispersion law at small q values: omega = omega(o) + Dq(2). At T-N. these modes change from a collective to a diffusive character. The width in energy associated to the quasielastic scattering exhibits a similar dispersion law: Gamma = Gamma(o) + dq(2). All these results are compared with other experimental results on similar compounds and discussed in the frame of existing theories. [S0163-1829(99)02241-9].