Quantized spin-wave modes in magnetic tunnel junction nanopillars
Quantized spin-wave modes in magnetic tunnel junction nanopillars
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DOI：
10.1103/physrevb.81.094416
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发表时间：
2009-07
影响因子：
3.7
通讯作者：
A. Helmer;S. Cornelissen;T. Devolder;J.-V. Kim;W. Roy;L. Lagae;C. Chappert
中科院分区：
文献类型：
--
作者：
A. Helmer;S. Cornelissen;T. Devolder;J.-V. Kim;W. Roy;L. Lagae;C. Chappert
我们提出了一个实验和理论研究的磁场依赖的热激发自旋波的模式频率的矩形纳米柱的横向尺寸为60\ifmmode\times\else\texttimes\fi {}100$，75\ifmmode\times\else\texttimes\fi {}150$，和105\ifmmode\times\else\texttimes\fi {} 190\text { }{\text{nm}}^{2}$，由基于MgO的磁性隧道结图案化。自旋波频率的测量使用光谱分辨的电噪声测量。在所有的光谱中，几个独立的量子化自旋波模式已被观察到，可以确定为本征激发的自由层和合成反铁磁体的结。使用的理论方法的基础上的对角化的三个耦合，空间受限的磁性层的系统的动力学矩阵，我们已经建模的最小的支柱的光谱，并提取其材料参数。CoFeB自由层的磁化强度和交换刚度常数由此被发现与相应的薄膜值相比大幅降低。此外，我们可以推断，在横向边界处的磁化钉扎一定很弱。最后，自由层和合成反铁磁体之间的层间偶极耦合导致模式anticrossings与间隙开口高达2 GHz。在低场和较大的支柱，有明显的证据表明，层的磁化强度的强不均匀性。特别地，在零场，最低模式不是基本模式，而是最可能位于层边缘附近的模式。
We present an experimental and theoretical study of the magnetic field dependence of the mode frequency of thermally excited spin waves in rectangular-shaped nanopillars of lateral sizes $60\ifmmode\times\else\texttimes\fi{}100$, $75\ifmmode\times\else\texttimes\fi{}150$, and $105\ifmmode\times\else\texttimes\fi{}190\text{ }{\text{nm}}^{2}$, patterned from MgO-based magnetic tunnel junctions. The spin-wave frequencies were measured using spectrally resolved electrical-noise measurements. In all spectra, several independent quantized spin-wave modes have been observed and could be identified as eigenexcitations of the free layer and of the synthetic antiferromagnet of the junction. Using a theoretical approach based on the diagonalization of the dynamical matrix of a system of three coupled, spatially confined magnetic layers, we have modeled the spectra for the smallest pillar and have extracted its material parameters. The magnetization and exchange stiffness constant of the CoFeB free layer are thereby found to be substantially reduced compared to the corresponding thin-film values. Moreover, we could infer that the pinning of the magnetization at the lateral boundaries must be weak. Finally, the interlayer dipolar coupling between the free layer and the synthetic antiferromagnet causes mode anticrossings with gap openings up to 2 GHz. At low fields and in the larger pillars, there is clear evidence for strong nonuniformities of the layer magnetizations. In particular, at zero field, the lowest mode is not the fundamental mode but a mode most likely localized near the layer edges.