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Bias-driven high-power microwave emission from MgO-based tunnel magnetoresistance devices

Abstract

Spin-momentum transfer between a spin-polarized current and a ferromagnetic layer can induce steady-state magnetization precession, and has recently been proposed as a working principle for ubiquitous radio-frequency devices for radar and telecommunication applications. However, so far, the development of industrially attractive prototypes has been hampered by the inability to identify systems that can provide enough power. Here, we demonstrate that microwave signals with device-compatible output power levels can be generated from a single magnetic tunnel junction with a lateral size of 100 nm, seven orders of magnitude smaller than conventional radio-frequency oscillators. We find that in MgO magnetic tunnel junctions the perpendicular torque induced by the spin-polarized current on the local magnetization can reach 25% of the in-plane spin-torque term, although showing a different bias dependence. Both findings contrast with the results obtained on all-metallic structures, previously investigated, reflecting the fundamentally different transport mechanisms in the two types of structure.

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Figure 1: Sample properties and principle of the experiment.
Figure 2: Spectra measured at 200 Oe and −250 Oe and positive (negative) currents between 0.1 (−0.1) mA and 1.1 (−1.1) mA with 0.1 mA steps.
Figure 3: TE-FMR: frequency shift with the current, peak-width dependence on the current and integrated power of the main peaks versus the square of the applied current.
Figure 4: Current-induced precession: current dependencies of peak frequency, power, and precession and tilt angles at −250 Oe and 200 Oe.
Figure 5: Parallel- and perpendicular-torque dependence on the bias.
Figure 6: Current–field phase diagram obtained by plotting the power integrated over the whole measured frequency range for each current and field.

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Acknowledgements

The authors thank J. C. Slonczewski, G. E. W. Bauer, T. J. Silva, S. E. Russek, M. Mizuguchi, R. Jansen and J. M. Shaw for discussions. This research was partially supported by SCOPE-MIC and MEXT. A.M.D. acknowledges support from the Japan Society for the Promotion of Science through the research grant P05330.

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Contributions

A.M.D. carried out the measurements, analysed the data and wrote the paper. A.F. and H.K. developed the patterning process and fabricated the samples. A.F. also provided considerable help with the experimental set-up. H.K., Y.N., K.T., D.D.D. and N.W. optimized the sputtering process for low-R A MgO magnetic tunnel junctions and deposited the multilayers. S.Y. helped develop the magnetic tunnel junction and carried out studies for increasing the TMR. Y.S. helped with analysing the data and calculated the losses in the system. All authors discussed the result and commented on the manuscript.

Corresponding author

Correspondence to Alina M. Deac.

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Supplementary Information

Supplementary Information, Supplementary Figures 1—8 and Supplementary Table 1 (PDF 732 kb)

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Deac, A., Fukushima, A., Kubota, H. et al. Bias-driven high-power microwave emission from MgO-based tunnel magnetoresistance devices. Nature Phys 4, 803–809 (2008). https://doi.org/10.1038/nphys1036

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