Measurement of Gilbert damping parameters in nanoscale CPP-GMR spin valves
Measurement of Gilbert damping parameters in nanoscale CPP-GMR spin valves
复制标题
纳米级 CPP-GMR 自旋阀吉尔伯特阻尼参数的测量
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
J. Childress
中科院分区：
文献类型：
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作者：
N. Smith;M. Carey;J. Childress
在60 nm直径的CPP-GMR自旋阀结构的IrMn/Ref/Cu/Free自旋阀堆栈中，用器件级原位测量了热磁噪声谱线宽，同时测定了这两个磁层的本征Gilbert衰减。结果表明，在自由层和参考层静态平衡磁化之间的“魔角”处仔细对准，可以在实际上没有自旋扭矩效应的情况下直接测量宽带本征热谱，否则自旋扭矩效应会严重扭曲谱线形状，并需要将线宽外推到零电流(然而，这也被证明与直接方法很好地一致)。实验魔角谱与宏观自旋计算和微磁本征模分析都有很好的定性和定量一致性。尽管成分和厚度相似，但人们反复发现IrMn交换钉扎参考层的本征Gilbert衰减(α~0.1)是自由层(α~0.01)的十倍。认为较大的参考层衰减是由于IrMn/REF对到有耗模的强非共振耦合，而不是通常所说的双磁振子过程。
In-situ, device level measurement of thermal mag-noise spectral linewidths in 60nm diameter CPP-GMR spin-valve stacks of IrMn/ref/Cu/free, with reference and free layer of similar CoFe/CoFeGe alloy, are used to simultaneously determine the intrinsic Gilbert damping for both magnetic layers. It is shown that careful alignment at a "magic-angle" between free and reference layer static equilibrium magnetization can allow direct measurement of the broadband intrinsic thermal spectra in the virtual absence of spin-torque effects which otherwise grossly distort the spectral line shapes and require linewidth extrapolations to zero current (which are nonetheless also shown to agree well with the direct method). The experimental magic-angle spectra are shown to be in good qualitative and quantitative agreement with both macrospin calculations and micromagnetic eigenmode analysis. Despite similar composition and thickness, it is repeatedly found that the IrMn exchange pinned reference layer has ten times larger intrinsic Gilbert damping (alpha ~ 0.1) than that of the free-layer (alpha ~ 0.01). It is argued that the large reference layer damping results from strong, off -resonant coupling to to lossy modes of an IrMn/ref couple, rather than commonly invoked two-magnon processes.