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ON Much of experimental studies on heteroepitaxial growth systems have led to a very attractive information which suggests the strong relevance of epitaxial strain in thin films on their electronic and magnetic properties. Some representative experimental observations include the enhancement of TC in superconducting La1.9Sr0.1CuO4 thin film, [1] the metalinsulator transition in CaRuO3 thin film, [2] and the colossal magnetoresistance in La0.67Ca0.33MnOx thin film. [3] The lattice strain, mostly generated by both lattice and thermal expansion mismatch in epitaxial film growth, changes cation order, [4, 5] stoichiometry, [2] and three dimensional strain state, [6, 7] which modulates the fundamental solid state phenomena such as electrical transport and magnetism. Therefore, the modification of the properties of novel perovskite oxide materials by lattice strain is of particular interest for both potential device application and understanding of solid state phenomena. Here, we present a new approach being responsible for lattice strain, i.e. structural transition induced strain, and a phenomenological explanation is attempted on its effects on electrical and magnetic properties. This approach is to control the properties of perovskite oxide materials of interest using biaxial strain induced by the phase transition of ferroelectric substrate material. EXPERIMENT For the study, the (100) BaTiO3 was chosen as a ferroelectric substrate. The BaTiO3 differs from the other ferroelectrics in that the phase transitions occur at lower temperatures with respect to PbTiO3 (TC = 763 K) or KNbO3 (TC = 708 K), i.e. transitions from paraelectric cubic to ferroelectric tetragonal at 393 K (=TC), then to orthorhombic at 278 K, and finally to rhombohedral at 183 K.[8] This allows the study of strain effects on the film material at low temperature regime below room temperature. As a film material, SrRuO3 with a bulk ferromagnetic Curie temperature (TC) of about 160 K [9] was selected to investigate the effect

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of strain due to the structural change of ferroelectric substrate on both electrical transport and magnetic properties. The SrRuO3 has an orthorhombic, GdFeO3 type structure with lattice parameters of a = 5.53 Å, b = 5.57 Å, and c = 7.85 Å, and a slightly distorted pseudocubic perovskite unit cell of ap = bp = cp = 3.93 Å. For convenience, this article is described on the basis of pseudocubic structure which has been recognized as a stable match with various perovskite oxides.[10] The SrRuO3 films were grown on (100) BaTiO3 substrates using 90° offaxis sputtering techniques. RESULTS As is expected, the films grown on BaTiO3 substrates have the strain due to lattice mismatch as well as that due to phase transitions of ferroelectric substrate. Both strain effects on the electrical transport were studied as a function of temperature by four terminal transport method. In order to investigate the effect of the strain due to lattice mismatch between the film and substrate on electrical transport, the films grown on (001) KTaO3 and