用自旋波光谱法测定横向磁化CoFeB层的交换刚度
Exchange stiffness in ultrathin perpendicularly-magnetized CoFeB layers determined using spin wave spectroscopy
摘要：
我们测量了纳米厚垂直磁化的FeCoB系统中自旋波的频率，并对频率进行建模，以推导出这种材料在磁共振极限下的交换刚度。为此，我们将磁性隧道结中的层图案化为直径范围从100到300 nm的圆形纳米柱，并且我们使用磁阻来确定哪些rf电流频率在填充自旋波模式中是有效的。微磁计算表明，该层的非线性和所使用的大波矢量确保自旋波频率主要由交换刚度决定，使得在给定频率窗口中的模式数可以用于估计交换。对于1 nm层，实验数据与交换刚度A= 20 pJ/m一致，这略低于其本体对应物。交换刚度的厚度依赖性对于涉及具有强磁化梯度的磁性膜及其微磁性描述的许多情况具有强烈的影响。
英文摘要：
We measure the frequencies of spin waves in nm-thick perpendicularly magnetized FeCoB systems, and model the frequencies to deduce the exchange stiffness of this material in the ultrathin limit. For this, we embody the layers in magnetic tunnel junctions patterned into circular nanopillars of diameters ranging from 100 to 300 nm and we use magneto-resistance to determine which rf-current frequencies are efficient in populating the spin wave modes. Micromagnetic calculations indicate that the ultrathin nature of the layer and the large wave vectors used ensure that the spin wave frequencies are predominantly determined by the exchange stiffness, such that the number of modes in a given frequency window can be used to estimate the exchange. For 1 nm layers the experimental data are consistent with an exchange stiffness A= 20 pJ/m, which is slightly lower that its bulk counterpart. The thickness dependence of the exchange stiffness has strong implications for the numerous situations that involve ultrathin films hosting strong magnetization gradients, and the micromagnetic description thereof.
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