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Magnetoresistance in granular films formed by CoFe and phase change material

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Abstract

Magnetoresistance having a field and current dependence like that of GMR (but a rather small magnitude) has been observed in Co70Fe30/GeTe and Co70Fe30/Ge2Sb2Te5 granular films. Film stacks were fabricated using tandem (multilayer) deposition and annealing was required for the films to develop the GMR-type response. This GMR-type behavior is distinct from AMR, which is observed before annealing. With films having the structure [CoFe 4 nm/GeTe 6 nm]10, a magnetoresistance (MR) of 0.19 %, which has the GMR-type character can be observed after an optimal annealing temperature of 450 °C. TEM and X-ray reflectometry suggest that columnar granules with layered Fe form during deposition and with annealing. Magnetoresistive transport is believed to be between the discontinuous layers in each columnar grain. These discontinuous layers are observed to be superparamagnetic in SQUID ZFC-FC measurements measured from 5–300 K. Magnetoresistance can be fitted by the quadratic relation appropriate for GMR in granular films, especially at higher GeTe compositions. When Ge2Sb2Te5 is used instead of GeTe, higher anneal temperatures are required before the MR with GMR character appears. This GMR type response does not appear when pure Fe is used instead of the CoFe alloy, with the samples showing only AMR in this case. This is due to the absence of Co which seems to cause a more granular growth.

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Acknowledgements

The authors wish to thank Law Leong Tat for his sputtering expertise. Huang would also like to thank the Agency for Science, Technology, and Research (A*STAR) for financial support.

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Authors and Affiliations

  1. Data Storage Institute, (A*STAR) Agency for Science, Technology and Research, DSI Building, 5 Engineering Drive 1, Singapore, 117608, Singapore

    J. C. Huang, W. D. Song, Y. Yang, L. P. Shi & T. C. Chong

  2. Department of Electrical and Computer Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, 15213-3890, USA

    J. C. Huang, J. A. Bain & T. E. Schlesinger

  3. Institute of Materials Research and Engineering, (A*STAR) Agency for Science, Technology and Research, 3, Research Link, Singapore, 117602, Singapore

    H. K. Hui

  4. Singapore University of Technology and Design, 20 Dover Drive, Singapore, 138682, Singapore

    T. C. Chong

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  1. J. C. Huang
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Huang, J.C., Song, W.D., Bain, J.A. et al. Magnetoresistance in granular films formed by CoFe and phase change material. Appl. Phys. A 113, 221–229 (2013). https://doi.org/10.1007/s00339-012-7522-1

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  • DOI: https://doi.org/10.1007/s00339-012-7522-1

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