We demonstrate changes in the saturation magnetization of Pd(001) ultrathin films exhibiting ferromagnetism in Pd/SrTiO3/BaTiO3 heterostructures due to the strain effect caused by the structural phase transition of BaTiO3 substrates. When a BaTiO3 substrate with a single domain formed by voltage application transitioned from the orthorhombic phase to the tetragonal phase, the saturation magnetization of Pd decreased by about 5%. The first-principles calculations, which assumed the distortion accompanied by the orthorhombic to the tetragonal structural phase transition, indicated a decrease by 3%–4% in the magnetization, which was consistent with the experimental results.

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Here, we would like to give a brief justification of the discussion. In both three and eight monolayers, magnetization decreased when BTO transitioned from the O phase to the T phase of BTO. In addition, Fig. 6 shows steep changes in DOS at εF in both phases. From these results, it can be expected that similar magnetization changes will also occur in thick films.

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