Journal of Electronic Materials

, Volume 45, Issue 6, pp 3200–3207 | Cite as

Thickness-, Composition-, and Magnetic-Field-Dependent Complex Impedance Spectroscopy of Granular-Type-Barrier Co/Co-Al2O3/Co MTJs

  • Nguyen Anh Tuan
  • Nguyen Tuan Anh
  • Nguyen Tuyet Nga
  • Nguyen Anh Tue
  • Giap  Van Cuong


The alternating-current (ac) electrical properties of granular-type-barrier magnetic tunnel junctions (GBMTJs) based on Co/Co x (Al2O3)1−x (t)/Co trilayer structures have been studied using complex impedance spectroscopy (CIS). Their CIS characteristics were investigated in external magnetic fields varying from 0 kOe to 3 kOe as a function of Co composition x at 10 at.%, 25 at.%, and 35 at.%, with barrier layer thickness t of 20 nm to 90 nm. The influence of these factors on the behaviors of the ac impedance response of the GBMTJs was deeply investigated and attributed to the dielectric or conducting nature of the Co-Al2O3 barrier layer. The most remarkable typical phenomena observed in these behaviors, even appearing paradoxical, include lower impedance for thicker t for each given x, a declining trend of Z with increasing x, a clear decrease of Z with H, and especially a partition of Z into zones according to the H value. All these effects are analyzed and discussed to demonstrate that diffusion-type and mass-transfer-type phenomena can be inferred from processes such as spin tunneling and Coulomb or spin blockade in the Co-Al2O3 barrier layer.


Granular-type-barrier MTJ hybrid-type MTJ complex impedance spectroscopy impedance response ac spin-dependent transport 


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This research is funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under Grant No. 103.02.2012.65.


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Copyright information

© The Minerals, Metals & Materials Society 2016

Authors and Affiliations

  • Nguyen Anh Tuan
    • 1
  • Nguyen Tuan Anh
    • 1
  • Nguyen Tuyet Nga
    • 2
  • Nguyen Anh Tue
    • 2
  • Giap  Van Cuong
    • 1
    • 3
  1. 1.International Training Institute for Materials Science (ITIMS)Hanoi University of Science and Technology (HUST)HanoiVietnam
  2. 2.Institute of Engineering Physics (IEP)Hanoi University of Science and Technology (HUST)HanoiVietnam
  3. 3.Faculty of Basic SciencesHung Yen University of Technology and Education (UTEHY)Khoai ChauVietnam

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