Strain-controlled responsiveness of slave half-doped manganite La0.5Sr0.5MnO3 layers inserted in BaTiO3 ferroelectric tunnel junctions

Insertion of layers displaying field-induced metal-to-insulator (M/I) transition in ferroelectric tunnel junctions (FTJs) has received attention as a potentially useful way to enlarge junction tunnel electroresistance (TER). Half-doped manganites being at the verge of metal-insulator character are thus good candidates to be slave layers in FTJs. However, the phase diagram of these oxides is extremely sensitive to strain and thus can be radically different when integrated in epitaxial FTJs. Here we report a systematic study of large-area (A = 4 to 100 um2) Pt/La0.5Sr0.5MnO3/BaTiO3/La0.7Sr0.3MnO3 (Pt/HD/BTO/LSMO) FTJs, having different thicknesses of the ferroelectric (2-3nm) and HD layers (1-2nm), grown on substrates imposing either tensile (SrTiO3) or compressive (LaAlO3) strains. Room-temperature electric characterization of the FTJs shows polarization-controlled ON/ OFF states. Clear evidences of field-induced M/I transition (difference between junction resistance in OFF and ON state is increased of more than one order of magnitude) are observed in junctions prepared on SrTiO3 but the HD layer is generally metallic on LaAlO3. Moreover, the M/I transition is only confined in an interfacial layer of the slave film thus entailing an overall reduction of TER. The orderly results reported here give some hints towards selection of HD materials and substrates for optimal FTJ responsiveness.