Effect of MgO Cap Layer on Gilbert Damping of FeB Electrode Layer in MgO-Based Magnetic Tunnel Junctions

We investigated the Gilbert damping of thin films with a MgO-barrier/Fe 80 B 20 /MgO-cap/Ta structure, in which the Fe 80 B 20 layer corresponds to a free layer of a perpendicularly magnetized magnetic tunnel junction, by using ferromagnetic resonance (FMR). We systematically varied the thickness of...

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Published inApplied physics express Vol. 6; no. 7; pp. 073002 - 073002-4
Main Authors Konoto, Makoto, Imamura, Hiroshi, Taniguchi, Tomohiro, Yakushiji, Kay, Kubota, Hitoshi, Fukushima, Akio, Ando, Koji, Yuasa, Shinji
Format Journal Article
LanguageEnglish
Published The Japan Society of Applied Physics 01.07.2013
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Summary:We investigated the Gilbert damping of thin films with a MgO-barrier/Fe 80 B 20 /MgO-cap/Ta structure, in which the Fe 80 B 20 layer corresponds to a free layer of a perpendicularly magnetized magnetic tunnel junction, by using ferromagnetic resonance (FMR). We systematically varied the thickness of the MgO cap layer and estimated the damping constant ($\alpha$) by measuring the dependence of the FMR spectrum on the magnetic field angle. The MgO cap layer was found to reduce $\alpha$ to about 0.005, which is less than half the value without the cap. The significant reduction can be explained by the suppression of spin pumping by the dielectric MgO cap layer.
Bibliography:High-resolution cross-sectional TEM images of buffer layers/MgO (1 nm)/FeB (2 nm)/MgO ($t_{\text{cap}}$)/Ta (10 nm) with (a) $t_{\text{cap}} = 0$ and (b) $t_{\text{cap}} = 1.4$ nm. (a) Typical examples of FMR spectra of Ta/MgO/FeB/MgO cap (1.1 nm)/Ta thin film at $\theta_{H} = 0$, 15, 30, and 90°. The definition of $\theta_{H}$ is shown in the inset of (b). Red and black lines indicate experimental data and least-squares fitting to an anti-Lorentzian function, respectively. (b) $\theta_{H}$ dependences of FMR resonance field ($H_{\text{R}}$) and peak-to-peak linewidth ($\Delta H_{\text{pp}}$). Red circles indicate experimental data, and thick green lines represent numerical fits. For $\Delta H_{\text{pp}}$, the contribution from intrinsic damping ($\Delta H_{\text{pp}}^{\alpha}$), distribution of effective demagnetization field ($\Delta H_{\text{pp}}^{4\pi M_{\text{eff}}}$), and two-magnon scattering ($\Delta H_{\text{pp}}^{\text{TMS}}$) are shown in the bottom panel. MgO cap thickness ($t_{\text{cap}}$) dependence of damping constant $\alpha$ for Ta/MgO/FeB/MgO cap/Ta films. Solid and broken lines are guides for the eye. $\theta_{H}$ dependences of peak-to-peak linewidth ($\Delta H_{\text{pp}}$) for $t_{\text{cap}} = 0$. The symbols are the same as those in Fig. (b).
ISSN:1882-0778
1882-0786
DOI:10.7567/APEX.6.073002