The rare earth gallium garnets Dy3Ga5O12, Gd3Ga5O12, Sm3Ga5O12, and Nd3Ga5O12used as substrate materials and the magnetic film materials EuEr2GaxFe5-xO12( ) and EuxEr3-xGa0.7Fe4.3O12( ) 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 (a0= lattice constant at 25°C, = lattice constant - a0versus shows a very slight concavity over the whole temperature interval with higher values of 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 have the same shape as the rare earth gallium garnets, but with higher values of 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 increase with increasing iron content. The implications of these observations on the properties of magnetic films for bubble domain applications are discussed.