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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73 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 languageEnglish
Article number023920
JournalJournal of Applied Physics
Volume106
Issue number2
DOIs
Publication statusPublished - 2009

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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