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Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions

Abstract

The tunnel magnetoresistance (TMR) effect in magnetic tunnel junctions (MTJs)1,2 is the key to developing magnetoresistive random-access-memory (MRAM), magnetic sensors and novel programmable logic devices3,4,5. Conventional MTJs with an amorphous aluminium oxide tunnel barrier, which have been extensively studied for device applications, exhibit a magnetoresistance ratio up to 70% at room temperature6. This low magnetoresistance seriously limits the feasibility of spintronics devices. Here, we report a giant MR ratio up to 180% at room temperature in single-crystal Fe/MgO/Fe MTJs. The origin of this enormous TMR effect is coherent spin-polarized tunnelling, where the symmetry of electron wave functions plays an important role. Moreover, we observed that their tunnel magnetoresistance oscillates as a function of tunnel barrier thickness, indicating that coherency of wave functions is conserved across the tunnel barrier. The coherent TMR effect is a key to making spintronic devices with novel quantum-mechanical functions, and to developing gigabit-scale MRAM.

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Figure 1: TEM images of a single-crystal MTJ with the Fe(001)/MgO(001)(1.8 nm)/Fe(001) structure.
Figure 2: Tunnel magnetoresistance of Fe(001)/MgO(001)/Fe(001) junctions.
Figure 3: Bias voltage—dependence of the TMR effect.

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Acknowledgements

We would like to thank M. Yamamoto, T. Katayama and Y. Yokoyama for their assistance with the experiments, and C. M. Boubeta, E. Tamura and H. Itoh for their helpful discussions.

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Correspondence to Shinji Yuasa.

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Yuasa, S., Nagahama, T., Fukushima, A. et al. Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions. Nature Mater 3, 868–871 (2004). https://doi.org/10.1038/nmat1257

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