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Sensors 2017, 17(10), 2424; https://doi.org/10.3390/s17102424

Effect of MgO Underlying Layer on the Growth of GaOx Tunnel Barrier in Epitaxial Fe/GaOx/(MgO)/Fe Magnetic Tunnel Junction Structure

1
National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Umezono 1-1-1, Central 2, Tsukuba, Ibaraki 305-8568, Japan
2
Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan
*
Author to whom correspondence should be addressed.
Received: 28 August 2017 / Revised: 28 September 2017 / Accepted: 20 October 2017 / Published: 23 October 2017
(This article belongs to the Special Issue GMR and TMR Sensors)
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Abstract

We investigated the effect of a thin MgO underlying layer (~3 monoatomic layers) on the growth of GaOx tunnel barrier in Fe/GaOx/(MgO)/Fe(001) magnetic tunnel junctions. To obtain a single-crystalline barrier, an in situ annealing was conducted with the temperature being raised up to 500 °C under an O2 atmosphere. This annealing was performed after the deposition of the GaOx on the Fe(001) bottom electrode with or without the MgO(001) underlying layer. Reflection high-energy electron diffraction patterns after the annealing indicated the formation of a single-crystalline layer regardless of with or without the MgO layer. Ex situ structural studies such as transmission electron microscopy revealed that the GaOx grown on the MgO underlying layer has a cubic MgAl2O4-type spinel structure with a (001) orientation. When without MgO layer, however, a Ga-Fe-O ternary compound having the same crystal structure and orientation as the crystalline GaOx was observed. The results indicate that the MgO underlying layer effectively prevents the Fe bottom electrode from oxidation during the annealing process. Tunneling magneto-resistance effect was observed only for the sample with the MgO underlying layer, suggesting that Ga-Fe-O layer is not an effective tunnel-barrier. View Full-Text
Keywords: magnetic tunnel junction; epitaxial growth; gallium oxide; tunneling magneto-resistance; semiconductor magnetic tunnel junction; epitaxial growth; gallium oxide; tunneling magneto-resistance; semiconductor
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Narayananellore, S.K.; Doko, N.; Matsuo, N.; Saito, H.; Yuasa, S. Effect of MgO Underlying Layer on the Growth of GaOx Tunnel Barrier in Epitaxial Fe/GaOx/(MgO)/Fe Magnetic Tunnel Junction Structure. Sensors 2017, 17, 2424.

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