Increased domain wall mobilities have been observed with increased gallium concentration in liquid phase epitaxial (LEE) films of Ga and/or Al substituted Eu3−xErxFe5012. As the total substitution is raised from about 0.7 to 1.8 of the 5 Fe ions, the Neel temperature, YN, decreases from 450 K to 320 K and the mobility rises from ∼25 to ∼450 cm/sec Oe. Reduced uniaxial anisotropy accounts for only a minor part of this increase in mobility. Reduction of the exchange energy by ∼25% in the low Neel temperature samples should give rise to a reduction of ∼13% in their mobilities, opposite to the observed change. Differences in thickness or magnetization between the samples do not correlate with the mobility changes. The coercivity decreases with TN, but this is probably not the cause of the increase in mobility. Variations of the g‐factor from ∼0.6 to >7 were observed in these materials but this increased g probably also does not account for the mobility increases. The relevant mechanisms could include reduced cubic anisotropy or changes of rare‐ earth energy levels and corresponding decreases in the wall damping. In these materials, the improved mobilities are achieved at the expense of inferior temperature sensitivity since the magnetic compensation point is raised above room temperature.