Spin excitations in [La1−xCaxMnO3] in the mixed-phase region

The magnetic excitations and the ferromagnetic order parameter have been studied by neutron scattering in a series of the manganese-based CMR perovskites [La1−xCaxMnO3] (x=0.46, 0.48, 0.50) near the metallic ferromagnetic to insulating antiferromagnetic phase. Well-defined ferromagnetic spin waves were detected for the x=0.46 and x=0.48 compositions. From the measurements of the order parameter, only the x=0.48 sample showed conclusive evidence of a coexistence of an antiferromagnetic phase with the ferromagnetic phase. For this composition, hysteresis was observed in the spin wave intensity but not in the spin stiffness parameter. This effect indicates that the ferromagnetic exchange is not perturbed by the antiferromagnetic ordering. No measurable ferromagnetic magnetization was found in the x=0.50 sample; thus no spin waves could be detected. The results indicate that the onset of the antiferromagnetism upon hole doping for the series occurs in a narrow region of x below the x=0.50 phase boundary.