Buffer-Layer Approach to High-Quality Fe₃O₄/BaTiO₃ Thin Films on MgO

An innovative two-step thin film growth approach for complex oxide heterostructures was verified using transmission electron microscopy (TEM, see Figure below). An initial low temperature (1023 K) nucleation buffer layer of BaTiO₃ (BTO) on high mismatch MgO substrate (~ 7% lattice misfit), was followed by a thicker BTO at higher temperature (1173 K), for subsequent growth of top magnetic Fe₃O₄ layer.

TEM studies show that most of the defects are accommodated by the initial BTO buffer, thereby relieving considerable strain in the second BTO layer. This facilitates smoother top (exposed) surface of BTO, which forms excellent epitaxy with Fe₃O₄, for further investigation of magneto-ferroelectric coupled phenomena.

Cube-on-cube orientation relations between various thin films and substrates:
[100]Fe₃O₄//[100]BaTiO₃//[100]MgO and (010)Fe₃O₄//(010)BaTiO₃//(010)MgO