TY - JOUR

T1 - Effect of Magnetic Coupling between Two CoFeB Layers on Thermal Stability in Perpendicular Magnetic Tunnel Junctions with MgO/CoFeB/Insertion Layer/CoFeB/MgO Free Layer

AU - Nishioka, K.

AU - Miura, S.

AU - Honjo, H.

AU - Naganuma, H.

AU - Nguyen, T. V.A.

AU - Watanabe, T.

AU - Ikeda, S.

AU - Endoh, T.

N1 - Publisher Copyright:
© 1965-2012 IEEE.

PY - 2022/2/1

Y1 - 2022/2/1

N2 - We investigated the effect of magnetic coupling (the energy constant of unit area Jcpl ) between CoFeB free layers on thermal stability factor Δ in magnetic tunnel junction (MTJ) with CoFeB/MgO double interfacial perpendicular magnetic anisotropy (IPMA). We newly introduced Jcpl in models for calculations, which were based on magnetic domain propagation model when MTJ diameter d is larger than critical diameter dc and magnetization coherent rotation model when d ≤ dc. With increasing Jcpl , Δ increases and saturates when Jcpl is over a critical value Jcplc. Magnetostatic coupling constants ( Jstat ) between the free layers were also calculated. Jstat is much smaller than Jcplc and cannot maximize Δ by itself, so an interlayer exchange coupling (the critical energy constant of unit area Jexc ) is required to cover the difference between Jcplc and Jstat. Jexc also rapidly increases with the decrease in d and reaches a plateau of 0.15 mJ/m2 in d ≤ 30 nm. MTJ devices with the smallest Jex(=0.01 mJ/m^2 ) and a moderate PMA (constant per unit area Keff t^∗ ) were made and Δ s were evaluated by experiments. The experimental Δ s were fitted by the calculations with adjusting stiffness constants A_s. The calculated Δ s and the experimental Δ s were in good agreement when A_s had a smaller value than that of the blanket film. Since the experimentally used Jex value was almost 0, Δ values were estimated when Jex was a greater value of 0.15 mJ/m2. As a result, 30% enhancement of Δ was obtained at the smallest d = 20 nm.

AB - We investigated the effect of magnetic coupling (the energy constant of unit area Jcpl ) between CoFeB free layers on thermal stability factor Δ in magnetic tunnel junction (MTJ) with CoFeB/MgO double interfacial perpendicular magnetic anisotropy (IPMA). We newly introduced Jcpl in models for calculations, which were based on magnetic domain propagation model when MTJ diameter d is larger than critical diameter dc and magnetization coherent rotation model when d ≤ dc. With increasing Jcpl , Δ increases and saturates when Jcpl is over a critical value Jcplc. Magnetostatic coupling constants ( Jstat ) between the free layers were also calculated. Jstat is much smaller than Jcplc and cannot maximize Δ by itself, so an interlayer exchange coupling (the critical energy constant of unit area Jexc ) is required to cover the difference between Jcplc and Jstat. Jexc also rapidly increases with the decrease in d and reaches a plateau of 0.15 mJ/m2 in d ≤ 30 nm. MTJ devices with the smallest Jex(=0.01 mJ/m^2 ) and a moderate PMA (constant per unit area Keff t^∗ ) were made and Δ s were evaluated by experiments. The experimental Δ s were fitted by the calculations with adjusting stiffness constants A_s. The calculated Δ s and the experimental Δ s were in good agreement when A_s had a smaller value than that of the blanket film. Since the experimentally used Jex value was almost 0, Δ values were estimated when Jex was a greater value of 0.15 mJ/m2. As a result, 30% enhancement of Δ was obtained at the smallest d = 20 nm.

KW - Magnetic coupling

KW - magnetic tunnel junction (MTJ)

KW - perpendicular anisotropy

KW - spin-transfer torque magnetoresistive random access memories (STT-MRAMs)

KW - thermal stability factor

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U2 - 10.1109/TMAG.2021.3083575

DO - 10.1109/TMAG.2021.3083575

M3 - Article

AN - SCOPUS:85107197063

VL - 58

JO - IEEE Transactions on Magnetics

JF - IEEE Transactions on Magnetics

SN - 0018-9464

IS - 2

ER -