Chen Yuan-Tsung, Chang Zu-Gao
Department of Materials Science and Engineering, I-Shou University, Kaohsiung 840, Taiwan.
Nanomaterials (Basel). 2013 Oct 15;3(4):574-582. doi: 10.3390/nano3040574.
This investigation studies CoFeB/AlO/Co magnetic tunneling junction (MTJ) in the magnetic field of a low-frequency alternating current, for various thicknesses of the barrier layer AlO. The low-frequency alternate-current magnetic susceptibility (χ) and phase angle (θ) of the CoFeB/AlO/Co MTJ are determined using an c 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 AlO and CoFeB as amorphous phases. The full width at half maximum (FWHM) of the Co(0002) peak, decreases as the AlO thickness increases; revealing that the Co layer becomes more crystalline with increasing thickness. χ result demonstrates that the optimal resonance frequency () that maximizes the χ 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 AlO 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 χ value. The results concerning magnetism indicate that the magnetic characteristics are related to the crystallinity of Co.
本研究针对不同厚度的势垒层AlO，在低频交流电磁场中对CoFeB/AlO/Co磁性隧道结（MTJ）展开研究。使用c分析仪测定CoFeB/AlO/Co MTJ的低频交流磁化率（χ）和相角（θ）。驱动频率范围为10至25000 Hz。这些多层MTJ利用直流和射频磁控溅射系统沉积在硅衬底上。势垒层厚度分别为22 Å、26 Å和30 Å。X射线衍射图谱（XRD）包括一个来自六方密堆积（HCP）Co的2θ = 44.7°主峰，具有高度（0002）织构结构，其中AlO和CoFeB为非晶相。Co(0002)峰的半高宽（FWHM）随AlO厚度增加而减小；这表明Co层随着厚度增加变得更加结晶。χ结果表明，使χ值最大化的最佳共振频率（）为500 Hz。当频率增加到1000 Hz时，磁化率迅速下降。然而，当频率超过1000 Hz时，磁化率急剧下降，几乎接近零。实验结果表明，在AlO势垒层厚度为30 Å时，平均最佳磁化率为1.87，这是因为Co(0002)织构诱导了磁各向异性，从而提高了间接CoFeB和Co自旋交换耦合强度以及χ值。有关磁性的结果表明，磁特性与Co的结晶度有关。
