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Susceptibility of CoFeB/AlO x /Co Magnetic Tunnel Junctions to Low-Frequency Alternating Current

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ABSTRACT

This investigation studies CoFeB/AlOx/Co magnetic tunneling junction (MTJ) in the magnetic field of a low-frequency alternating current, for various thicknesses of the barrier layer AlOx. The low-frequency alternate-current magnetic susceptibility (χac) and phase angle (θ) of the CoFeB/AlOx/Co MTJ are determined using an χac analyzer. The driving frequency ranges from 10 to 25,000 Hz. These multilayered MTJs are deposited on a silicon substrate using a DC and RF magnetron sputtering system. Barrier layer thicknesses are 22, 26, and 30 Å. The X-ray diffraction patterns (XRD) include a main peak at 2θ = 44.7° from hexagonal close-packed (HCP) Co with a highly (0002) textured structure, with AlOx and CoFeB as amorphous phases. The full width at half maximum (FWHM) of the Co(0002) peak, decreases as the AlOx thickness increases; revealing that the Co layer becomes more crystalline with increasing thickness. χac result demonstrates that the optimal resonance frequency (fres) that maximizes the χac value is 500 Hz. As the frequency increases to 1000 Hz, the susceptibility decreases rapidly. However, when the frequency increases over 1000 Hz, the susceptibility sharply declines, and almost closes to zero. The experimental results reveal that the mean optimal susceptibility is 1.87 at an AlOx barrier layer thickness of 30 Å because the Co(0002) texture induces magneto-anisotropy, which improves the indirect CoFeB and Co spin exchange-coupling strength and the χac value. The results concerning magnetism indicate that the magnetic characteristics are related to the crystallinity of Co.

No MeSH data available.


Mean optimal susceptibility and average phase angle as functions of AlOx barrier thickness.
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nanomaterials-03-00574-f005: Mean optimal susceptibility and average phase angle as functions of AlOx barrier thickness.

Mentions: Figure 5 plots the mean optimal susceptibility and phase angle for AlOx barriers with thicknesses of 22, 26, and 30 Å. The average phase angle corresponds to the mean optimal susceptibility. It is 49.07°, 94.94°, and 156.71°, at thicknesses of 22, 26, and 30 Å, respectively. From Table 1 and Figure 5, the mean optimal susceptibility increases from 1.19 to 1.87 as the average phase angle varies form 49.07° to 156.71°. The mean maximum χac and phase angle increase with the AlOx barrier thickness because the magneto-anisotropy of Co(0002) texture induces strong indirect spin exchange coupling between CoFeB and Co, increasing χac. The results in Figure 5 also indicate that χac increases with the phase angle. The χac and the phase angle follow vary similarly. Moreover, an increasing phase angle is associated with increasingly sensitive to spin exchange-coupling strength, which is observed as a high susceptibility.


Susceptibility of CoFeB/AlO x /Co Magnetic Tunnel Junctions to Low-Frequency Alternating Current
Mean optimal susceptibility and average phase angle as functions of AlOx barrier thickness.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5304595&req=5

nanomaterials-03-00574-f005: Mean optimal susceptibility and average phase angle as functions of AlOx barrier thickness.
Mentions: Figure 5 plots the mean optimal susceptibility and phase angle for AlOx barriers with thicknesses of 22, 26, and 30 Å. The average phase angle corresponds to the mean optimal susceptibility. It is 49.07°, 94.94°, and 156.71°, at thicknesses of 22, 26, and 30 Å, respectively. From Table 1 and Figure 5, the mean optimal susceptibility increases from 1.19 to 1.87 as the average phase angle varies form 49.07° to 156.71°. The mean maximum χac and phase angle increase with the AlOx barrier thickness because the magneto-anisotropy of Co(0002) texture induces strong indirect spin exchange coupling between CoFeB and Co, increasing χac. The results in Figure 5 also indicate that χac increases with the phase angle. The χac and the phase angle follow vary similarly. Moreover, an increasing phase angle is associated with increasingly sensitive to spin exchange-coupling strength, which is observed as a high susceptibility.

View Article: PubMed Central - PubMed

ABSTRACT

This investigation studies CoFeB/AlOx/Co magnetic tunneling junction (MTJ) in the magnetic field of a low-frequency alternating current, for various thicknesses of the barrier layer AlOx. The low-frequency alternate-current magnetic susceptibility (χac) and phase angle (θ) of the CoFeB/AlOx/Co MTJ are determined using an χac analyzer. The driving frequency ranges from 10 to 25,000 Hz. These multilayered MTJs are deposited on a silicon substrate using a DC and RF magnetron sputtering system. Barrier layer thicknesses are 22, 26, and 30 Å. The X-ray diffraction patterns (XRD) include a main peak at 2θ = 44.7° from hexagonal close-packed (HCP) Co with a highly (0002) textured structure, with AlOx and CoFeB as amorphous phases. The full width at half maximum (FWHM) of the Co(0002) peak, decreases as the AlOx thickness increases; revealing that the Co layer becomes more crystalline with increasing thickness. χac result demonstrates that the optimal resonance frequency (fres) that maximizes the χac value is 500 Hz. As the frequency increases to 1000 Hz, the susceptibility decreases rapidly. However, when the frequency increases over 1000 Hz, the susceptibility sharply declines, and almost closes to zero. The experimental results reveal that the mean optimal susceptibility is 1.87 at an AlOx barrier layer thickness of 30 Å because the Co(0002) texture induces magneto-anisotropy, which improves the indirect CoFeB and Co spin exchange-coupling strength and the χac value. The results concerning magnetism indicate that the magnetic characteristics are related to the crystallinity of Co.

No MeSH data available.