Shift registers based on magnetic domain wall ratchets with perpendicular anisotropy

Abstract

The movement of magnetic domain walls can be used to build a device known as a shift register, which has applications in memory1 and logic circuits2,3. However, the application of magnetic domain wall shift registers has been hindered by geometrical restrictions, by randomness in domain wall displacement and by the need for high current densities or rotating magnetic fields. Here, we propose a new approach in which the energy landscape experienced by the domain walls is engineered to favour a unidirectional ratchet-like propagation. The domain walls are defined between domains with an out-of-plane (perpendicular) magnetization, which allows us to route domain walls along arbitrary in-plane paths using a time-varying applied magnetic field with fixed orientation. In addition, this ratchet-like motion causes the domain walls to lock to discrete positions along these paths, which is useful for digital devices. As a proof-of-principle experiment we demonstrate the continuous propagation of two domain walls along a closed-loop path in a platinum/cobalt/platinum strip.

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Figure 1: Domain wall ratchet shift register.
Figure 2: Demonstration of the ratchet effect in a platinum/cobalt/platinum strip.
Figure 3: Proof-of-principle operation of two domain walls in a circular loop.
Figure 4: Statistics of ratchet operation as a function of pulse duration and amplitude.

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Acknowledgements

This work is part of the research programme of the Foundation for Fundamental Research on Matter (FOM), which is part of the Netherlands Organisation for Scientific Research (NWO).

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J.H.F. devised the concept, designed and performed the experiments, performed the data analysis and prepared the manuscript. H.J.M.S. and B.K. accommodated the experiments, assisted in the analysis and commented on the final manuscript.

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Correspondence to J. H. Franken.

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The authors declare no competing financial interests.

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Franken, J., Swagten, H. & Koopmans, B. Shift registers based on magnetic domain wall ratchets with perpendicular anisotropy. Nature Nanotech 7, 499–503 (2012). https://doi.org/10.1038/nnano.2012.111

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