Annealing effect of magnetic tunnel junctions with one FeOx layer inserted at the Al[sub 2]O[sub 3]/CoFe interface

Zhang, Zongzhi; Cardoso, Susana; Freitas, P. P.; Wei, P.; Barradas, N.; Soares, J. C.
May 2001
Applied Physics Letters;5/7/2001, Vol. 78 Issue 19, p2911
Academic Journal
Spin tunnel junctions with one interposed Fe oxide layer between the Al[sub 2]O[sub 3] barrier (t[sub Al]=8-9 Å) and the top CoFe pinned layer show large tunneling magnetoresistance (TMR) values (39%) after 40 min anneal at 380 °C. The as-deposited TMR is low and does not increase until 350 °C (<10%), but then increases sharply, peaking at 380°C. Further anneals at this temperature (380 °C), lead to TMR decrease to 20% with a diffusion constant of 34 min. At 360 °C, the diffusion constant is about 60 min. Samples without this inserted FeOx layer show TMR<5% after prolonged anneals at 380 °C. The different techniques utilized to probe the barrier and electrode changes during the annealing processes indicate that from the initial Fe-FeOx layer, part of the Fe diffuses into the CoFe electrode, and the remaining FeOx probably decomposes into a pure interfacial Fe layer at high temperature, responsible for the large TMR. The observed TMR values and barrier parameters, seem consistent with a standard CoFe/Al[sub 2]O[sub 3]/CoFe barrier formed at high temperature. © 2001 American Institute of Physics.


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