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Spin-torque diode effect in magnetic tunnel junctions

Abstract

There is currently much interest in the development of ‘spintronic’ devices, in which harnessing the spins of electrons (rather than just their charges) is anticipated to provide new functionalities that go beyond those possible with conventional electronic devices. One widely studied example of an effect that has its roots in the electron's spin degree of freedom is the torque exerted by a spin-polarized electric current on the spin moment of a nanometre-scale magnet. This torque causes the magnetic moment to rotate1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19 at potentially useful frequencies. Here we report a very different phenomenon that is also based on the interplay between spin dynamics and spin-dependent transport, and which arises from unusual diode behaviour. We show that the application of a small radio-frequency alternating current to a nanometre-scale magnetic tunnel junction20,21,22 can generate a measurable direct-current (d.c.) voltage across the device when the frequency is resonant with the spin oscillations that arise from the spin-torque effect: at resonance (which can be tuned by an external magnetic field), the structure exhibits different resistance states depending on the direction of the current. This behaviour is markedly different from that of a conventional semiconductor diode23, and could form the basis of a nanometre-scale radio-frequency detector in telecommunication circuits.

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Figure 1: Experimental set-up and magnetoresistance.
Figure 2: Direct-current voltage generated by the device in response to the alternating current.
Figure 3: Magnetic-field dependence of microwave power and a.c. current dependence of d.c. voltage.
Figure 4: Principle of the spin-torque diode.

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Acknowledgements

A.A.T. thanks the Japan Society for the Promotion of Science for the fellowship grant. S.Y. thanks the Japan Science and Technology Agency (JST) for the PRESTO programme. A part of this work is supported by the 21st Century COE programme by JSPS. We thank C. Chappert, T. Devolder, W. Mizutani and M. Mizuguchi for their help.

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Correspondence to Y. Suzuki.

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Supplementary information

Supplementary Discussion 1

This shows the derivation equation 1 (dc voltage generated by passing ac current) and the last equation in the text. (DOC 65 kb)

Supplementary Figure 1

This figure shows the high field magnetization data of a typical film used for making MTJs. The coupling between the various layers can be obtained form this. (PDF 19 kb)

Supplementary Figure 2

This figure shows a fit to the dc voltage by equation 1 in the text. The ratio of spin-transfer to the effective field term can be extracted from the fit. (PDF 48 kb)

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Tulapurkar, A., Suzuki, Y., Fukushima, A. et al. Spin-torque diode effect in magnetic tunnel junctions. Nature 438, 339–342 (2005). https://doi.org/10.1038/nature04207

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