AVS 53rd International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI-WeA

Invited Paper MI-WeA8
Tunnel Magnetoresistance Effect in Sputtered MTJs with MgO Barrier and Various Ferromagnetic Electrodes

Wednesday, November 15, 2006, 4:20 pm, Room 2006

Session: Exchange Bias & TMR
Presenter: J. Hayakawa, Hitachi Ltd. and Tohoku University, Japan
Authors: J. Hayakawa, Hitachi Ltd. and Tohoku University, Japan
S. Ikeda, Tohoku University, Japan
Y.M. Lee, Tohoku University, Japan
R. Sasaki, Tohoku University, Japan
T. Meguro, Tohoku University, Japan
F. Matsukura, Tohoku University, Japan
H. Takahashi, Hitachi Ltd., Japan and Tohoku University, Japan
H. Ohno, Tohoku University, Japan
Correspondent: Click to Email
Magnetic tunnel junctions (MTJs) with a crystalline MgO barrier offer giant tunnel magnetoresistance (TMR) ratio@footnote 1-5@ and current-induced magnetization reversal at low critical current and are of considerable interest in terms of physics involved as well as of application to advanced magnetic memories (MRAMs). Here we report high TMR ratio over 360% at room temperature in (100) oriented CoFeB/MgO/CoFeB MTJ sputtered on Si/SiO wafers. The MTJs consist of Ta (5nm) / NiFe (5nm) / MnIr (10nm) / CoFe (2nm) / Ru (0.8nm) / CoFeB (3nm) / MgO / CoFe(B) / Ta (5nm) / Ru (5nm). The thickness of the MgO barrier was varied from 0.80 to 2.4 nm. We found that the TMR ratio increases with increasing the annealing temperature (Ta), and reaches 361% at RT when the Ta is 400°C (578% at 5 K). These TMR ratios correspond to tunneling spin-polarizations of 0.80 and 0.86 by using Julliere's formula. HRTEM images revealed that the as-deposited CoFeB electrodes were amorphous and the as-deposited MgO barrier had highly (001)-oriented NaCl structure with good uniformity. The images also showed that by annealing at 375°C, full crystallization of the CoFeB ferromagnetic electrodes in body centered cubic structure took place. The observed giant TMR ratio is attributed to the formation of highly (100) oriented crystalline MTJs with an MgO barrier and bcc CoFeB by annealing, which satisfies the conditions for high TMR ratio predicted by the theoretical studies.@footnote 6-8@ We will also show the tunnel magnetoresistance effect in the MTJs with CoFe-B free layers with different Co, Fe, and B (Boron) compositions. This work was supported by the IT-program of Research Revolution 2002 (RR2002): Development of Universal Low-power Spin Memory, Ministry of Education, Culture, Sports, Science and Technology of Japan. @FootnoteText@@footnote 1@S. Yuasa, T. Nagahama, A. Fukushima, Y. Suzuki, and K. Ando, Nat. Mater. 868, 3 (2004). @footnote 2@S. S. Parkin, C. Kaiser, A. Panchula, P. M. Rice, B. Hughes, M. Samant, and S.-H. Yang: Nat. Mater. 3, 862 (2004). @footnote 3@D. D. Djayaprawira, K. Tsunekawa, M. Nagai, H. Maehara, S. Yamagata, N. Watanabe, S. Yuasa, Y. Suziki, and K. Ando, Appl. Phys. Lett. 86, 092502 (2005). @footnote 4@J. Hayakawa, S. Ikeda, Y. M. Lee, R. Sasaki, T. Meguro, F. Matsukura, H. Takahashi, and H. Ohno, Jpn. J. Appl. Phys, 44, L1267 (2005). @footnote 5@S. Ikeda, J. Hayakawa, Y. M. Lee, R. Sasaki, T. Meguro, F. Matsukura, and H. Ohno, Jpn. J. Appl. Phys, 44, L1442 (2005). @footnote 6@W. H. Butler, X.-G. Zhang, T. C. Schulthess and J. M. MacLaren, Phys. Rev. B. 63, 054416 (2001). @footnote 7@J. Mathon and a. Umersky, Phys. Rev. B. 63, 220403R (2005). @footnote 8@X.-G Zhang and W. H. Butler, Phys. Rev. B 70, 172407 (2004).