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Tunnel junctions with multiferroic barriers

Abstract

Multiferroics are singular materials that can exhibit simultaneously electric and magnetic orders. Some are ferroelectric and ferromagnetic and provide the opportunity to encode information in electric polarization and magnetization to obtain four logic states. However, such materials are rare and schemes allowing a simple electrical readout of these states have not been demonstrated in the same device. Here, we show that films of La0.1Bi0.9MnO3 (LBMO) are ferromagnetic and ferroelectric, and retain both ferroic properties down to a thickness of 2 nm. We have integrated such ultrathin multiferroic films as barriers in spin-filter-type tunnel junctions that exploit the magnetic and ferroelectric degrees of freedom of LBMO. Whereas ferromagnetism permits read operations reminiscent of magnetic random access memories (MRAM), the electrical switching evokes a ferroelectric RAM write operation. Significantly, our device does not require the destructive ferroelectric readout, and therefore represents an advance over the original four-state memory concept based on multiferroics.

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Figure 1: Schematic representation of the tunnel barrier potential profiles and tunnel currents for a ferromagnetic and a ferroelectric barrier.
Figure 2: Magnetic and ferroelectric properties of 30 nm LBMO films.
Figure 3: Magnetic and ferroelectric properties of ultrathin LBMO films.
Figure 4: Tunnel magnetoresistance of LBMO-based spin-filters and temperature dependence of the tunnel magnetoresistance and electroresistance.
Figure 5: Tunnel electroresistance and its combination with tunnel magnetoresistance in LBMO-based spin filters, defining a four-resistance-state system.

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Acknowledgements

We thank M. Varela and E. Jacquet for their help in sample fabrication and N. D. Mathur, J. F. Scott and H. Kohlstedt for fruitful discussions. This study was partially supported by the Picasso France–Spain program, the CICYT of the Spanish Government Projects NAN2004-9094 and MAT2005-05656, FEDER, the E.U. Marie Curie mobility program, the project FEMMES of the French Agence National de la Recherche (ANR-05-1-45147), the European Science Foundation THIOX network and the E.U. STREPs Nanotemplates (Contract NMPA4-2004-505955) and MaCoMuFi (Contract FP6-NMP3-CT-2006-033221).

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Correspondence to Manuel Bibes.

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Gajek, M., Bibes, M., Fusil, S. et al. Tunnel junctions with multiferroic barriers. Nature Mater 6, 296–302 (2007). https://doi.org/10.1038/nmat1860

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