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Enhanced tunnelling electroresistance effect due to a ferroelectrically induced phase transition at a magnetic complex oxide interface

Abstract

The range of recently discovered phenomena in complex oxide heterostructures, made possible owing to advances in fabrication techniques, promise new functionalities and device concepts1,2,3. One issue that has received attention is the bistable electrical modulation of conductivity in ferroelectric tunnel junctions4,5,6 (FTJs) in response to a ferroelectric polarization of the tunnelling barrier, a phenomenon known as the tunnelling electroresistance (TER) effect7,8,9,10. Ferroelectric tunnel junctions with ferromagnetic electrodes allow ferroelectric control of the tunnelling spin polarization through the magnetoelectric coupling at the ferromagnet/ferroelectric interface11,12,13,14,15,16,17. Here we demonstrate a significant enhancement of TER due to a ferroelectrically induced phase transition at a magnetic complex oxide interface. Ferroelectric tunnel junctions consisting of BaTiO3 tunnelling barriers and La0.7Sr0.3MnO3 electrodes exhibit a TER enhanced by up to ~ 10,000% by a nanometre-thick La0.5Ca0.5MnO3 interlayer inserted at one of the interfaces. The observed phenomenon originates from the metal-to-insulator phase transition in La0.5Ca0.5MnO3, driven by the modulation of carrier density through ferroelectric polarization switching. Electrical, ferroelectric and magnetoresistive measurements combined with first-principles calculations provide evidence for a magnetoelectric origin of the enhanced TER, and indicate the presence of defect-mediated conduction in the FTJs. The effect is robust and may serve as a viable route for electronic and spintronic applications.

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Figure 1: Device geometry, atomic structure and polarization-induced charge accumulation in FTJs.
Figure 2: Transport properties of FTJs.
Figure 3: Ferroelectric and magnetoresistive properties of FTJs.
Figure 4: Results of density functional calculations.

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Acknowledgements

The work at Pennsylvania State University (PSU) was supported in part by the DOE (Grant No. DE-FG02-08ER4653) and the NSF (Grant No. DMR-1207474). The PSU NSF MRSEC seed grant and NNIN Nanofabrication facilities are acknowledged. The work at USTC was supported by NBRP-2012CB922003 and NSFC. The work at the University of Nebraska-Lincoln (UNL) was supported by NSF MRSEC (Grant No. DMR-0820521) and NSF EPSCoR (Grant No. EPS-1010674). Computations were performed at the UNL Holland Computing Center. The work at ORNL was supported by the Materials Science and Engineering Division of the US DOE.

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Contributions

E.Y.T. and J.D.B. predicted the magnetoelectrically induced TER effect and stimulated the experimental studies. Q.L. designed and supervised the experiment. Y.W.Y. fabricated samples and performed transport measurements. Q.L., Y.W.Y. and X.G.L. analysed the data. Y-M.K. and A.Y.B. carried out STEM and EELS measurements in the laboratory led by S.J.P. S.M.Y. performed PFM measurements under the supervision of T.W.N. A.G. assisted in analysing the PFM data. J.D.B. carried out theoretical calculations under the supervision of E.Y.T. Q.L., E.Y.T., Y.W.Y. and J.D.B. wrote the manuscript. All authors contributed to the refinement of the manuscript.

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Correspondence to E. Y. Tsymbal or Qi Li.

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Yin, Y., Burton, J., Kim, YM. et al. Enhanced tunnelling electroresistance effect due to a ferroelectrically induced phase transition at a magnetic complex oxide interface. Nature Mater 12, 397–402 (2013). https://doi.org/10.1038/nmat3564

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