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The rare earth gallium garnets Dy3Ga5O12, Gd3Ga5O12, Sm3Ga5O12, and Nd3Ga5O12used as substrate materials and the magnetic film materials EuEr2GaxFe5-xO12(0 \leq x \leq 5) and EuxEr3-xGa0.7Fe4.3O12(0 \leq x \leq 3) have been prepared and their lattice parameters measured between room temperature and 1200°C. In the series R3Ga5O12, the room temperature lattice constant decreases linearly in the order Nd>Sm>Gd>Dy. The curve\Deltaa/a_{0}(a0= lattice constant at 25°C,\Deltaa= lattice constant - a0versusTshows a very slight concavity over the whole temperature interval with higher values of\Deltaa/a_{0}in the same order as the room temperature lattice constants. The lattice constants follow Vegard's law with the substitution of europium for erbium in the series EuxEr3-xGa0.7Fe4.3O12and decrease with decreasing europium content. The curves of\Deltaa/a_{0}have the same shape as the rare earth gallium garnets, but with higher values of\Deltaa/a_{0}in the opposite order to the room temperature lattice constants. Substitution of gallium for iron in the series EuEr2GaxFe5-xO12caused positive deviation from Vegard's law and a decrease in the room temperature lattice constants. The values of\Deltaa/a_{0}increase with increasing iron content. The implications of these observations on the properties of magnetic films for bubble domain applications are discussed.