Effect of annealing temperature on formation of superparamagnetism in CoFeB/MgO/CoFeB magnetic tunnel junctions

•The annealing effect of CoFeB/MgO/CoFeB magnetic tunnel junctions with a thin free layer was studied.•With increasing annealing temperature, the transfer curves transform from hysteresis to hysteresis-free behavior.•The transformation depends not only on the thickness, but also on the annealing tem...

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Bibliographic Details
Published in:Applied surface science 2014-09, Vol.314, p.443-446
Main Authors: Cao, Jiangwei, Liu, Yan, Ren, Yang, Wei, Fulin, Freitas, P.P.
Format: Article
Language:English
Subjects:
Annealing
Condensed matter: electronic structure, electrical, magnetic, and optical properties
Condensed matter: structure, mechanical and thermal properties
Cross-disciplinary physics: materials science
rheology
Diffusion
Exact sciences and technology
Formations
Hysteresis
Magnesium oxide
Magnetic tunnel junction
Mathematical analysis
Physics
Superparamagnetism
Thin films
Transformations
Tunnel junctions
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Summary:•The annealing effect of CoFeB/MgO/CoFeB magnetic tunnel junctions with a thin free layer was studied.•With increasing annealing temperature, the transfer curves transform from hysteresis to hysteresis-free behavior.•The transformation depends not only on the thickness, but also on the annealing temperature and annealing time.•The MR loops without hysteresis originate from the superparamagnetic behavior of the free layer. We report the annealing effect of CoFeB/MgO/CoFeB magnetic tunnel junctions with a thin free layer. For the junctions with CoFeB free layer below the critical thickness, the MR transfer curves are always hysteresis-free and TMR ratio decreases with increasing annealing temperature. For the junctions with CoFeB free layer above the critical thickness, with increasing annealing temperature, both TMR ratio and coercivity increase firstly and then decrease, and finally hysteresis-free MR transfer curves are obtained. The MR loops without hysteresis can be well fitted by using the Langevin equation, suggesting the formation of superparamagnetic particles in the free layer during the high temperature annealing. This behavior originates from the transformation of the ultra-thin CoFeB free layer during annealing: crystallization process of CoFeB and diffusion at MgO/CoFeB and CoFeB/Ru interfaces.
ISSN:0169-4332
1873-5584
DOI:10.1016/j.apsusc.2014.07.015