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Nanoscale patterning of complex magnetic nanostructures by reduction with low-energy protons

Nature Nanotechnology volume 7, pages 567–571 (2012)Cite this article

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Abstract

Techniques that can produce patterns with nanoscale details on surfaces have a central role in the development of new electronic1,2,3, optical4,5,6 and magnetic7,8,9,10 devices and systems. High-energy ion irradiation can produce nanoscale patterns on ferromagnetic films by destroying the structure of layers or interfaces10,11,12,13,14,15,16,17,18, but this approach can damage the film and introduce unwanted defects13,14. Moreover, ferromagnetic nanostructures that have been patterned by ion irradiation often interfere with unpatterned regions through exchange interactions, which results in a loss of control over magnetization switching15,16,17,18. Here, we demonstrate that low-energy proton irradiation can pattern an array of 100-nm-wide single ferromagnetic domains by reducing [Co3O4/Pd]10 (a paramagnetic oxide) to produce [Co/Pd]10 (a ferromagnetic metal). Moreover, there are no exchange interactions in the final superlattice, and the ions have a minimal impact on the overall structure, so the interfaces between alternate layers of cobalt (which are 0.6 nm thick) and palladium (1.0 nm) remain intact. This allows the reduced [Co/Pd]10 superlattice to produce a perpendicular magnetic anisotropy that is stronger than that observed in the metallic [Co/Pd]10 superlattices we prepared for reference. We also demonstrate that our non-destructive approach can reduce CoFe2O4 to metallic CoFe.

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Figure 1: Non-destructive magnetic nanopatterning.
Figure 2: Effects of proton irradiation on the magnetic properties of [Co3O4/Pd]10 superlattices.
Figure 3: Microstructures of the superlattices.
Figure 4: Magnetic characteristics of nanopatterned superlattices irradiated at a dose of 4.3 × 1020 ions per m2.

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Change history

  • 09 August 2012

    In the version of this Letter originally published online, on page 1 'structure' was incorrectly used instead of 'texture' in the sentence "…and has a face-centred-cubic (fcc) (311) texture." Also an extraneous '1' appeared on page 2 in the sentence "Note that cobalt hydroxide is paramagnetic at room temperature and antiferromagnetic below ∼12 K." The authors also wish to correct some further problems: On page 2, the word 'glazing' should have been 'grazing' in the sentence "…cobalt hydroxide are observed under grazing incident synchronous X-ray scattering…". On page 4, the phrase 'and high coercivity' should not have appeared in the sentence "…the patterns demonstrate strong PMA — a squareness of unity — just as we find in…". In the first line of the Methods section, the phrase 'thermally oxidized' was missing in the sentence "Superlattices were deposited on a thermally oxidized Si(100) substrate using…". All these errors have now been corrected in all versions of the Letter.

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Acknowledgements

The authors thank E. Sullivan, Y. Jo, D.R. Lee, H-J. Shin, H.H. Lee, K-H. Yoo, M-H. Cho, D-H. Ko, I. Sohn, T. Emery, S-J. Park and M. Ahn for help with measurements and discussions. The authors also thank H. Youn and C-Y. Chung (Park System Corporation) for their support in observing magnetic images using MFM, and T.W. Lee (RIAM) for his support with XRD and XRR measurements. This research was supported in part by the Basic Science Research Program (2011-0003263), the Pioneer Research Center Program (2011-000-2116) and the Center for Nanoscale Mechatronics and Manufacturing (which is one of the 21st Century Frontier Research Programs (2011K000243) funded by the Korean Ministry of Education, Science and Technology).

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Authors and Affiliations

  1. Materials Science and Engineering, Yonsei University, Seoul, 120-749, Korea

    Sanghoon Kim, Soogil Lee, Jungho Ko, Jangyup Son, Minseok Kim & Jongill Hong

  2. Mechanical Engineering, Yonsei University, Seoul, 120-749, Korea

    Shinill Kang

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Contributions

S.Ki. and J.H. conceived and designed the study. S.Ki. fabricated all patterns and carried out experiments, with the help of J.H. Contributions to the measurements were made by S.Ka., S.L., J.K., J.S. and M.K. All authors contributed to discussions regarding the research. S.Ki. and J.H. wrote the manuscript.

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Correspondence to Jongill Hong.

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Kim, S., Lee, S., Ko, J. et al. Nanoscale patterning of complex magnetic nanostructures by reduction with low-energy protons. Nature Nanotech 7, 567–571 (2012). https://doi.org/10.1038/nnano.2012.125

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