Multiferroic thin films are used as barriers in tunnel junctions to produce four-state memory devices
The recent revival of interest in multiferroics — materials exhibiting both ferromagnetic and ferroelectric properties — raises the possibility of realizing fast, low-power consumption, multifunctional memory devices exploiting the best attributes of conventional ferroelectric and magnetic random-access memories. The major hurdle to overcome, however, is the synthesis of suitable multiferroic materials exhibiting ferroelectricity at extremely small thicknesses.
Now, Manuel Bibes and colleagues1 of the Université-Sud, France and the Universitat Autonoma de Barcelona, Bellaterra, Spain have used pulsed laser deposition to produce lanthanum bismuth manganite (LBMO) thin films that are multiferroic down to thicknesses of 2 nm. A 40-nm-thick barrier of LBMO was placed between two electrodes and the variation of the resistance of the resulting tunnel junction was measured as a function of the bias voltage (tunnel electroresistance) and bias magnetic field (tunnel magnetoresistance). The junction exhibited large electro- and magnetoresistances and the combination of these two effects produced a four-resistance-state device that can be interrogated non-destructively by simply monitoring its resistance.
These results may find applications in spintronic based quantum-computing architectures, although using the LBMO material system described here would require cooling to liquid nitrogen temperatures.
References
Gajek, M. et al. Tunnel junctions with multiferroic junctions. Nature Mater. 10.1038/nmat1860 (2007).
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Sandhu, A. Thin dividing line. Nature Nanotech (2007). https://doi.org/10.1038/nnano.2007.83
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DOI: https://doi.org/10.1038/nnano.2007.83