Symmetry Does Not Allow Canting of Spins in La_{1.4}Sr_{1.6}Mn₂O₇

We analyze the symmetry of all possible magnetic structures of bilayered manganites La_{2-2x}Sr_{1+2x}Mn_2O_7 with doping 0.3 <= x < 0.5 and formulate a corresponding Landau theory of the phase transitions involved. It is shown that canting of spins is not allowed at x=0.3 though is at x=0.4. The observed magnetic reflections from the sample with x=0.3 may be described as arising from two spatially distributed phases with close transition temperatures but different easy axes and ranges of stability. Experimental results are revisited on the basis of the theoretical findings.