Ogasawara Takahiro, Oogane Mikihiko, Al-Mahdawi Muftah, Tsunoda Masakiyo, Ando Yasuo
Department of Applied Physics, Tohoku University, Sendai, 980-8579, Japan.
Center for Science and Innovation in Spintronics (Core Research Cluster) Organization for Advanced Studies, Tohoku University, Sendai, 980-8577, Japan.
Sci Rep. 2019 Nov 19;9(1):17018. doi: 10.1038/s41598-019-53439-0.
We studied the effect of second-order magnetic anisotropy on the linear conductance output of magnetic tunnel junctions (MTJs) for magnetic-field-sensor applications. Experimentally, CoFeB/MgO/CoFeB-based MTJs were fabricated, and the nonlinearity, NL was evaluated for different thicknesses, t of the CoFeB free layer from the conductance. As increasing t from 1.5 to 2.0 nm, maximum NL, NL was found to decrease from 1.86 to 0.17% within the dynamic range, H = 1.0 kOe. For understanding the origin of such NL behavior, a theoretical model based on the Slonczewski model was constructed, wherein the NL was demonstrated to be dependent on both the normalized second-order magnetic anisotropy field of H/|H| and the normalized dynamic range of H/|H|. Here, H, H, are the effective and second-order magnetic anisotropy field of the free layer in MTJ. Remarkably, experimental NL plotted as a function of H/|H| and H/|H|, which were measured from FMR technique coincided with the predictions of our model. Based on these experiment and calculation, we conclude that H is the origin of NL and strongly influences its magnitude. This finding gives us a guideline for understanding NL and pioneers a new prospective for linear-output MTJ sensors to control sensing properties by H.
我们研究了二阶磁各向异性对用于磁场传感器应用的磁隧道结（MTJ）线性电导输出的影响。通过实验制备了基于CoFeB/MgO/CoFeB的MTJ，并根据电导对不同厚度t的CoFeB自由层的非线性度NL进行了评估。当t从1.5增加到2.0nm时，发现在动态范围H = 1.0kOe内，最大非线性度NL从1.86%降至0.17%。为了理解这种NL行为的起源，构建了一个基于Slonczewski模型的理论模型，其中证明NL既取决于归一化的二阶磁各向异性场H/|H|，也取决于归一化的动态范围H/|H|。这里，H、H分别是MTJ中自由层的有效磁各向异性场和二阶磁各向异性场。值得注意的是，通过铁磁共振技术测量得到的实验NL作为H/|H|和H/|H|的函数绘制的曲线与我们模型的预测结果相符。基于这些实验和计算，我们得出结论，H是NL的起源并强烈影响其大小。这一发现为理解NL提供了指导方针，并为通过H控制传感特性的线性输出MTJ传感器开创了新的前景。
