Temperature Dependence of Tunnel Magnetoresistance in Co-Mn-Al/Al-Oxide/Co-Fe Junctions

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  • Oogane Mikihiko
    Department of Applied Physics, Graduate School of Engineering, Tohoku University
  • Nakata Jun
    Department of Applied Physics, Graduate School of Engineering, Tohoku University
  • Kubota Hitoshi
    Nanoelectronics Research Institute, AIST
  • Ando Yasuo
    Department of Applied Physics, Graduate School of Engineering, Tohoku University
  • Sakuma Akimasa
    Department of Applied Physics, Graduate School of Engineering, Tohoku University
  • Miyazaki Terunobu
    Department of Applied Physics, Graduate School of Engineering, Tohoku University

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Abstract

We investigated the temperature dependence of the tunnel magnetoresistance (TMR) effect in Co–Mn–Al/Al–oxide/Co–Fe tunnel junctions. The junction prepared without exposure to air during deposition showed very large TMR ratios of 65% at 10 K and 40% at room temperature. In contrast, the junction prepared with air exposure before and after Al–oxide layer fabrication showed a maximum TMR ratio of only 40% at a low temperature. Temperature dependences of tunnel conductance of these junctions were analyzed using a simple model that incorporates two contributions: elastic tunneling with decreasing spin polarization as temperature increases and spin-independent hopping tunneling through trap states in Al–oxide tunnel barriers. Results of analyses indicated that air exposure drastically reduced spin polarization and Curie temperature. It also created an inferior insulating layer at the Co–Mn–Al/Al–oxide interface.

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