Current-induced magnetization switching in MgO barrier magnetic tunnel junctions with CoFeB-based synthetic ferrimagnetic free layers

Jun Hayakawa, Shoji Ikeda, Katsuya Miura, Michihiko Yamanouchi, Young Min Lee, Ryutaro Sasaki, Masahiko Ichimura, Kenchi Ito, Takayuki Kawahara, Riichiro Takemura, Toshiyasu Meguro, Fumihiro Matsukura, Hiromasa Takahashi, Hideyuki Matsuoka, Hideo Ohno

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Abstract

We investigated the effect of using a synthetic ferrimagnetic (SyF) free layer in MgO-based magnetic tunnel junctions (MTJs) on current-induced magnetization switching (CIMS), particularly for application to spin-transfer torque random access memory (SPRAM). The employed SyF free layer had a Co 40Fe40B20/Ru/Co40Fe 40B20 and Co20Fe60B 20/Ru/Co20Fe60B20 structures, and the MTJs (100 × (150-300) nm2) were annealed at 300°C. The use of SyF free layer resulted in low intrinsic critical current density (J c0) without degrading the thermal-stability factor (E/kBT, where E, kB, and T are the energy potential, the Boltzmann constant, and temperature, respectively). When the two CoFeB layers of a strongly antiferromagnetically coupled SyF free layer had the same thickness, J c0 was reduced to 2-4 × 106 A/cm2. This low Jc0 may be due to the decreased effective volume under the large spin accumulation at the CoFeB/Ru. The E/kBT was over 60, resulting in a retention time of over ten years and suppression of the write current dispersion for SPRAM. The use of the SyF free layer also resulted in a bistable (parallel/antiparallel) magnetization configuration at zero field, enabling the realization of CIMS without the need to apply external fields to compensate for the offset field.

Original languageEnglish
Article number4544915
Pages (from-to)1962-1967
Number of pages6
JournalIEEE Transactions on Magnetics
Volume44
Issue number7
DOIs
Publication statusPublished - 2008 Jul 1

Keywords

  • CoFeB
  • Current-induced magnetization switching
  • MgO barrier
  • Synthetic ferrimagnetic free layer

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Electrical and Electronic Engineering

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    Hayakawa, J., Ikeda, S., Miura, K., Yamanouchi, M., Lee, Y. M., Sasaki, R., Ichimura, M., Ito, K., Kawahara, T., Takemura, R., Meguro, T., Matsukura, F., Takahashi, H., Matsuoka, H., & Ohno, H. (2008). Current-induced magnetization switching in MgO barrier magnetic tunnel junctions with CoFeB-based synthetic ferrimagnetic free layers. IEEE Transactions on Magnetics, 44(7), 1962-1967. [4544915]. https://doi.org/10.1109/TMAG.2008.924545