Multiferroic BiFeO 3 -based thin films were heteroepitaxially grown on LaNiO 3 /LaFeO 3 /MgO͑001͒ substrates by radio frequency magnetron sputtering. The epitaxial BFO-based films were grown with pure perovskite phase and a cube-on-cube relationship at a low processing temperature of 450°C. The partial substitution of La ions for Bi ions increased lattice parameters of the BFO film. With the La substitution, the significant improvement in dielectric, ferroelectric, and magnetic properties of the BFO films was observed.Magnetoelectric multiferroics have attracted considerable attention in current studies for their simultaneous ferroelectricity, ferromagnetism, and ferroelasticity. 1-6 These materials which have electric, magnetic, and structural order parameters in the same phase are rarely observed in nature because ferroelectricity is not compatible with ferromagnetism. The magnetism originated from the d-electrons of transition metal, which reduce the off-center tendency of ferroelectric materials. 1 BiFeO 3 ͑BFO͒ crystallizes in a rhombohedrally distorted perovskite structure with both ferroelectric ͑T C = 1103 K͒ and anti-ferromagnetic ͑T N = 643 K͒ characteristics. 3-10 The specific characteristics, such as a simple crystal structure, a high Curie temperature, and a high Néel temperature, are advantageous for research and various applications.Recently, Wang et al. reported dramatically enhanced multiferroic performance of epitaxial BFO films fabricated on SrRuO 3 -buffered SrTiO 3 substrates. 3,4 A dramatic enhancement of ferroelectric performance and magnetoelectric behavior were found to result from epitaxial-induced transition. 3,4 The excellent ferroelectric properties and magnetoelectric behavior of the BFO films provide an alternative choice of lead-free ferroelectric materials. 5,6 However, some challenges, including leakage problems, 7 high electric coercivity, 3-6,8-10 and inhomogeneous magnetic spin structure, 11,12 are necessary to be overcome in future applications. In previous studies, the leakage problems were markedly improved by well-controlled chemistry and interface of BFO films. 10,13 However, high electric coercivity and inhomogeneous magnetic spin structure of BFO films lead to difficulty of polarization switching and cancellation of macroscopic magnetization. 11 Previous studies suggest that electric coercivity 14-16 and inhomogeneous spin structure 17-19 can be effectively improved by La substitution. Therefore, the influence of La substitution on multiferroic properties of the epitaxial BFO films deserves more attention.Most epitaxial BFO-based films have been fabricated by pulsedlaser deposition ͑PLD͒ methods, at high processing temperatures above 670°C. 3-5,7,8 A low-temperature process of sputtering method is a promising method for growing bismuth-based materials without problems such as interdiffusion, phase decomposition, and chemical fluctuations. 13,20 This study reports the low-temperature preparation of the epitaxial BFO-based films by radio frequency ͑rf͒-magnetron sputterin...