Transmission electron microscopy investigation of CoFeB/MgO/CoFeB pseudospin valves annealed at different temperatures

S. V. Karthik; Y. K. Takahashi; T. Ohkubo; K. Hono; S. Ikeda; H. Ohno

doi:10.1063/1.3182817

Transmission electron microscopy investigation of CoFeB/MgO/CoFeB pseudospin valves annealed at different temperatures

S. V. Karthik, Y. K. Takahashi, T. Ohkubo, K. Hono, S. Ikeda, H. Ohno

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86 Citations (Scopus)

Abstract

We have investigated the microstructure and local chemistry of Ta/Ru/Ta/CoFeB/MgO/CoFeB/Ta/Ru magnetic tunnel junctions with different values of tunneling magnetoresistance (TMR) as a result of annealing at different temperatures. Annealing at 500 °C led to the templated crystallization of the amorphous CoFeB layer having coherent interfaces with MgO grains with an orientation relationship of 〈 001 〉 [011]_MgO∥ 〈 001 〉 [001]_CoFe, and the B rejected from crystallized CoFeB was found to be dissolved in upper amorphous Ta layers and segregated in the bottom crystalline Ta layer. Annealing at 600 °C led to the dissolution of 3-4 at. % Ta in the MgO barrier, and B was found to be segregated at the CoFeB/MgO and Ta/Ru interfaces as a result of the crystallization of the top amorphous Ta layer. Further degradation in TMR of the samples annealed at 650 °C results from the loss of bcc-CoFe (001) texture in the bottom CoFeB electrode due to the pronounced Ta diffusion into the CoFe/MgO/CoFe layers.

Original language	English
Article number	023920
Journal	Journal of Applied Physics
Volume	106
Issue number	2
DOIs	https://doi.org/10.1063/1.3182817
Publication status	Published - 2009
Externally published	Yes

ASJC Scopus subject areas

Physics and Astronomy(all)

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title = "Transmission electron microscopy investigation of CoFeB/MgO/CoFeB pseudospin valves annealed at different temperatures",

abstract = "We have investigated the microstructure and local chemistry of Ta/Ru/Ta/CoFeB/MgO/CoFeB/Ta/Ru magnetic tunnel junctions with different values of tunneling magnetoresistance (TMR) as a result of annealing at different temperatures. Annealing at 500 °C led to the templated crystallization of the amorphous CoFeB layer having coherent interfaces with MgO grains with an orientation relationship of 〈 001 〉 [011]MgO∥ 〈 001 〉 [001]CoFe, and the B rejected from crystallized CoFeB was found to be dissolved in upper amorphous Ta layers and segregated in the bottom crystalline Ta layer. Annealing at 600 °C led to the dissolution of 3-4 at. % Ta in the MgO barrier, and B was found to be segregated at the CoFeB/MgO and Ta/Ru interfaces as a result of the crystallization of the top amorphous Ta layer. Further degradation in TMR of the samples annealed at 650 °C results from the loss of bcc-CoFe (001) texture in the bottom CoFeB electrode due to the pronounced Ta diffusion into the CoFe/MgO/CoFe layers.",

author = "Karthik, {S. V.} and Takahashi, {Y. K.} and T. Ohkubo and K. Hono and S. Ikeda and H. Ohno",

note = "Funding Information: S.V.K. acknowledges the International Center for Materials Nanoarchitronics (MANA) for providing the MANA post doctorate fellowship. This work was in part supported by a Grant-in-Aid for Scientific Research in Priority Area “Creation and Control of Spin Current,” by the World Premier Research Center Initiative (WPI Initative) on Materials Nanoarchitectronics, MEXT, Japan, and by “High-Performance Low-Power Consumption Spin Devices and Storage Systems” program under Research and Development for Next-Generation Information Technology of MEXT.",

year = "2009",

doi = "10.1063/1.3182817",

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AU - Karthik, S. V.

AU - Takahashi, Y. K.

AU - Ohkubo, T.

AU - Hono, K.

AU - Ikeda, S.

AU - Ohno, H.

N1 - Funding Information: S.V.K. acknowledges the International Center for Materials Nanoarchitronics (MANA) for providing the MANA post doctorate fellowship. This work was in part supported by a Grant-in-Aid for Scientific Research in Priority Area “Creation and Control of Spin Current,” by the World Premier Research Center Initiative (WPI Initative) on Materials Nanoarchitectronics, MEXT, Japan, and by “High-Performance Low-Power Consumption Spin Devices and Storage Systems” program under Research and Development for Next-Generation Information Technology of MEXT.

PY - 2009

Y1 - 2009

N2 - We have investigated the microstructure and local chemistry of Ta/Ru/Ta/CoFeB/MgO/CoFeB/Ta/Ru magnetic tunnel junctions with different values of tunneling magnetoresistance (TMR) as a result of annealing at different temperatures. Annealing at 500 °C led to the templated crystallization of the amorphous CoFeB layer having coherent interfaces with MgO grains with an orientation relationship of 〈 001 〉 [011]MgO∥ 〈 001 〉 [001]CoFe, and the B rejected from crystallized CoFeB was found to be dissolved in upper amorphous Ta layers and segregated in the bottom crystalline Ta layer. Annealing at 600 °C led to the dissolution of 3-4 at. % Ta in the MgO barrier, and B was found to be segregated at the CoFeB/MgO and Ta/Ru interfaces as a result of the crystallization of the top amorphous Ta layer. Further degradation in TMR of the samples annealed at 650 °C results from the loss of bcc-CoFe (001) texture in the bottom CoFeB electrode due to the pronounced Ta diffusion into the CoFe/MgO/CoFe layers.

AB - We have investigated the microstructure and local chemistry of Ta/Ru/Ta/CoFeB/MgO/CoFeB/Ta/Ru magnetic tunnel junctions with different values of tunneling magnetoresistance (TMR) as a result of annealing at different temperatures. Annealing at 500 °C led to the templated crystallization of the amorphous CoFeB layer having coherent interfaces with MgO grains with an orientation relationship of 〈 001 〉 [011]MgO∥ 〈 001 〉 [001]CoFe, and the B rejected from crystallized CoFeB was found to be dissolved in upper amorphous Ta layers and segregated in the bottom crystalline Ta layer. Annealing at 600 °C led to the dissolution of 3-4 at. % Ta in the MgO barrier, and B was found to be segregated at the CoFeB/MgO and Ta/Ru interfaces as a result of the crystallization of the top amorphous Ta layer. Further degradation in TMR of the samples annealed at 650 °C results from the loss of bcc-CoFe (001) texture in the bottom CoFeB electrode due to the pronounced Ta diffusion into the CoFe/MgO/CoFe layers.

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Transmission electron microscopy investigation of CoFeB/MgO/CoFeB pseudospin valves annealed at different temperatures

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