(a) The synchrotron x-ray diffraction patterns (typical 222, 440, and 800 peaks, with wavelength of 0.413677 Å) for Gd_0.9Tb_0.1Fe₂, Gd_0.7Tb_0.3Fe₂, Gd_0.5Tb_0.5Fe₂ at room temperature. The resonant black, blue, and red lines are the experimental XRD data and the thinner red and blue lines are the fitted ones. (b) Rhombohedral symmetry with corresponding lattice parameters. The red arrow shows the easy magnetization direction of the rhombohedral phase.