Canted antiferromagnetism in an insulating lightly doped La_1-xSr_xMnO₃ with x⩽0.17

We have investigated the magnetic structure of an insulating lightly doped La_1-xSr_xMnO₃ with x=0.04,0.125, and 0.17 with neutron scattering technique and bulk magnetization measurements. The magnetic structure of the x=0.04 sample at 5 K is a commensurate layer-type (A-type) antiferromagnetism with the propagation vector [010] and the moment of 3.7±0.2μ_B/Mn, being parallel to the [100] axis in the orthorhombic Pnma symmetry. In addition, a spontaneous magnetization of 0.28±0.02μ_B/Mn is observed at 8 K by magnetization measurement. By contrast, the x=0.125 sample exhibits a large ferromagnetic moment of 3.7±0.2μ_B/Mn and a small A-type antiferromagnetic component of 0.23±0.1μ_B/Mn, while the x=0.17 sample exhibits only a ferromagnetic component of 3.6±0.2μ_B/Mn. These results are consistent with a spin structure derived from the conventional double exchange mechanism, but rule out the possibility of a recently suggested spiral spin structure for the insulating La_1-xSr_xMnO₃ system. © 1996 The American Physical Society.