Magnetic damping of the free layer of CoFeB in the spin valve IrMn/CoFe/Cu/CoFeB with large exchange bias has been characterized by frequency-swept ferromagnetic resonance under a series of fixed magnetic fields. The damping constant shows little difference between the parallel and antiparallel magnetization configurations, consistent with the theoretical prediction. Remarkably, in the intermediate states of the pinned CoFe layer under reversal, the effective damping constant of the CoFeB layer is significantly enhanced from 0.0119 up to 0.0292. This enhancement, exceeding the effect of the pumped spin current appreciably, is mainly due to the inhomogeneous broadening and/or two-magnon scattering caused by the stray field emerging from the domain walls (DW) of the pinned CoFe layer when its magnetization is partially reversed. Meanwhile, a resonance frequency shift is also observed in the presence of DW. Our result confirms the strong influence of the pinned layer DW on the magnetic damping in spin valves, which should be properly excluded while dealing with the nonlocal spin-transport-induced damping in heterostructures.

自旋阀IrMn / CoFe / Cu / CoFeB中CoFeB自由层的磁阻尼具有大的交换偏置，其特征是在一系列固定磁场下通过频率扫描铁磁谐振。阻尼常数在平行和反平行磁化配置之间几乎没有差异，与理论预测一致。值得注意的是，在被钉扎的CoFe层处于反转状态的中间状态下，CoFeB层的有效阻尼常数从0.0119显着提高到0.0292。这种增强明显超过了泵浦的自旋电流的影响，主要是由于固定的CoFe层的磁化部分地从固定的CoFe层的畴壁（DW）产生的杂散场引起的不均匀展宽和/或两磁子散射逆转。同时，在存在DW的情况下也观察到共振频率偏移。我们的结果证实了固定层DW对自旋阀的磁阻尼的强烈影响，在处理异质结构中非局部自旋传输引起的阻尼时，应适当排除该影响。