Spinel films of MnZn ferrite were grown by liquid phase epitaxy on MnGa2O4 substrates under controlled mixtures of H2 and CO2. Each layer was deposited at 660°C from a single Na2B4O7 based charge. Film composition varied with the growth ambient; CO2 atmospheres yielded films with a nominal composition of Mn.9Zn.5Fe1.6O4 and Curie temperatures near 110°C. As the oxygen partial pressure in the growth ambient was reduced by the addition of H2 to the CO2, film composition changed, the Fe content increased while the proportions of Mn and Zn decreased. As a result of the change in composition, film strain went from tensile to compressive and the magnetic properties varied. Film homogeneity also improved significantly with addition of H2 to the growth ambient. A H2/CO2 volume ratio of 1 to 10 produced films whose composition was nominally Mn.3Zn.3Fe2.4O4 and which had Curie temperatures of about 430°C. As H2 was added, film magnetization increased and induced magnetic anisotropy changed from easy axis to easy plane. In-plane coercivity was not simply related to growth ambient and varied between 8 and 18 Oe. The influence of the oxygen partial pressure on the growth process is interpreted in terms of the oxidation states of the Fe and Mn cations in the flux. © 1980, All rights reserved.